Preparation and adsorption properties of nano magnetite silica gel for methylene blue from aqueous solution

Premise setting for sustainable developing adsorption in environmental remediation using graphitic carbon nitride@agar-derived porous carbon composite

In the adsorption process for wastewater treatment, the adsorbent plays an important role. A composite adsorptive material composed of graphitic carbon nitride and agar-derived porous carbon (CNPC) was fabricated from simple precursors (melamine, thiourea, and agar) and through a facile procedure with different melamine and thiourea ratios. Characterization of CNPC proved a successful formation of a porous structure consisting of mesopores and macropores, wherein CNPC holds distinctive electrochemical (lowered resistance and higher specific capacity) and photochemical properties (lowered bandgap to 2.33 eV) thanks to the combination of graphitic carbon nitride (CN) and agar-derived porous carbon (PC). Inheriting the immanent nature, CNPC was subjected to the adsorption of methylene blue (MB) dye in an aqueous solution. The highest adsorption capacity was 133 mg/g for CNPC-4 which was prepared using a melamine to thiourea ratio of 4:4 - equivalent to the removal rate of 53.2 % and following the pseudo-I-order reaction rate. The effect of pH points out that pH 7 and 9 were susceptible to maximum removal and pretreatment is not required while the optimal ratio of 7.5 mg of MB and 30 mg of material was also determined to yield the highest performance. Furthermore, the reusability of the material for three consecutive cycles was evaluated based on two methods pyrolysis at 200 °C and photocatalytic degradation by irradiation under visible light. In general, the photocatalytic regeneration pathway is more ample and efficient than pyrolysis in terms of energy efficiency (saving energy over 10 times) and adsorption capacity stability. As a whole, the construction of accessible regenerative and stable adsorbent could be a venturing step into the sustainable development spearhead for industries.

Preparation and Characterization of Fe3O4/Poly(HEMA-co-IA) Magnetic Hydrogels for Removal of Methylene Blue from Aqueous Solution

In the present study, Fe3O4/poly(2-hydroxyethyl methacrylate-co-itaconic acid) magnetic hydrogels (MHGs) were prepared by in situ synthesis of Fe3O4 magnetic particles in hydrogels (HGs). The resulting magnetic hydrogels were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), a vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), and N2 adsorption-desorption. The effect of Fe3O4 on the swelling behavior and adsorption of methylene blue (MB) dye of the prepared hydrogel was studied. Parameters such as the dose, pH, contact time, and MB initial concentration were investigated. The results show that 75% (HG) and 91% (MHG) of MB (200 mg/L) were removed at doses of 2 mg/mL and 1 mg/mL, respectively, under a pH of 6.8 and a contact time of 10 min. The adsorption behavior followed the Langmuir isotherm model, indicating that the adsorption process takes place in monolayers and on homogeneous surfaces. The Langmuir capacities for MB adsorption using the HGs and MHGs were 78 and 174 mg/g, respectively. The adsorption kinetics followed a pseudo-second-order kinetic model. In addition, thermodynamic studies carried out show that the adsorption process is spontaneous and endothermic. Adsorption-desorption studies indicate that the magnetic hydrogel can remove MB for four cycles with removal efficiencies above 90%. Therefore, a MHG is suitable as an alternative material for MB adsorption.

Superior removal of methylene blue using green fabricated pomegranate peel/nano-hematite composite: reusability, isotherm and kinetics study

Green hematite nanoparticles were synthesized using pomegranate peel extract of different concentrations (2 g, 4 g, and 6 g) and in the presence of the peel residuals. The obtained products defined as PP/GNH (I), PP/GNH (II), and PP/GNH (III) referring to the hematite nanoparticles at different concentrations compositing with pomegranate peel residuals. The products were addressed as green adsorbents for methylene blue dye contaminants in water. They exhibit superior adsorption properties with theoretical q_max of 666, 1111, and 909 mg/g for PP/GNH (I), PP/GNH (II), and PP/GNH (III), respectively. The equilibration times were attained after 480 min for the three products. The isotherm and kinetic studies indicate that the adsorption systems for the synthetic materials are of chemisorption type. The adsorption behaviors of these systems can be demonstrated according to Pseudo-second order as well as Elovich kinetic model. Furthermore, the adsorption results reflected a mono-layer uptake form which was more suitable for the Langmuir model than other investigated models. The products also showed high performances when it comes to remove the dyes investigated such as methylene blue Congo red, safranin, methyl orange, and crystal violet. Finally, green fabricated nano hematite/pomegranate peel composites are of high stability and can be reused for five cycles.Communicated by Ramaswamy H. Sarma.

Insights into Coproduction of Silica Gel via Desulfurization of Steel Slag and Silica Gel Adsorption Performance

Steel slag is a calcium-containing alkaline industrial solid waste that can replace limestone for flue gas desulfurization. It can remove SO₂ and coproduce silica gel while avoiding CO₂ emission from limestone in the desulfurization process. In this study, steel slag with a D ₅₀ of 3.15 μm was used to remove SO₂. At room temperature, with a solid-liquid ratio of 1:10, a stirring speed of 800 rpm, and the mixed gas introduced at a flow rate of 0.8 mL/min, 1 ton of steel slag could remove 406.7 kg of SO₂, a SO₂ removal efficiency typical of existing calcium-rich desulfurizers. As limestone desulfurization can release CO₂, when limestone desulfurization was replaced with steel slag of equal desulfurization ratio, CO₂ emissions could be reduced by 279.6 kg and limestone could be reduced by 635.5 kg. The yield of silica gel was 5.1%. Silica gel pore structure parameters were close to those of commercially available B silica gel. Products after desulfurization were mainly CaSO₄ ·2H₂O, CaSO₄ ·0.5H₂O, CaSO₃ ·0.5H₂O, and silica gel. With a silica gel dosage of 30 mg, a temperature of 20 °C, a pH value of 6.00, a stirring time of 0.5 h, and a methylene blue concentration of 0.020 mg/mL, the removal ratio of methylene blue adsorbed by silica gel was 98.4%.

Fabrication and physical properties of a novel macroporous poly(vinyl alcohol)/cellulose fibre product

The objective of this work was to prepare functionalized cellulose fiber from sugar cane leaf (SCF) used to produce novel biomaterial. The SCF was treated with chloroacetic acid and sodium hydroxide (NaOH) to produce a modified cellulose fibre (MSCF). At higher MSCF loading, a greater porous density was observed under SEM. The addition of MSCF improved, the water resistance of the cured PVA/MSCF in both acid and base media through chemical reactions. The moisture absorption and moisture content of the cured PVA/MSCF film increased as the loading increased MSCF. Tg of the cured PVA/MSCF showed a clear decrease that was attributed to the greater molecular weight and softness of the molecular chains. The cured PVA/MSCF showed good MB absorption from wastewater. The improvement in biodegradability of the cured PVA/MSCF film may make it a candidate material for use in environmentally-sensitive applications.

Removal of Mercury (II) by EDTA-Functionalized Magnetic CoFe2O4@SiO2 Nanomaterial with Core-Shell Structure

In order to reduce the difficulty and risk of operation, decrease the preparation time and improve the adsorption performance of magnetic nano-silicon adsorbent with core-shell structure, a carboxylated CoFe₂O₄@SiO₂ was prepared by EDTA-functionalized method using a safe, mild and simple hydrothermal method. The results show that the prepared material of CoFe₂O₄@SiO₂-EDTA has a maximum adsorption capacity of 103.3 mg/g for mercury ions (Hg(II)) at pH = 7. The adsorption process of Hg(II) is a chemical reaction involving chelation and single-layer adsorption, and follows the pseudo-second-order kinetic and Langmuir adsorption isotherm models. Moreover, the removal of Hg(II) is a spontaneous and exothermic reaction. The material characterization, before and after adsorption, shows that CoFe₂O₄@SiO₂-EDTA has excellent recyclability, hydrothermal stability and fully biodegradable properties. To summarize, it is a potential adsorption material for removing heavy metals from aqueous solutions in practical applications.

Amine Modification of Silica Aerogels/Xerogels for Removal of Relevant Environmental Pollutants

Serious environmental and health problems arise from the everyday release of industrial wastewater effluents. A wide range of pollutants, such as volatile organic compounds, heavy metals or textile dyes, may be efficiently removed by silica materials advanced solutions such as aerogels. This option is related to their exceptional characteristics that favors the adsorption of different contaminants. The aerogels performance can be selectively tuned by an appropriate chemical or physical modification of the aerogel's surface. Therefore, the introduction of amine groups enhances the affinity between different organic and inorganic contaminants and the silica aerogels. In this work, different case studies are reported to investigate and better understand the role of these functional groups in the adsorption process, since the properties of the synthesized aerogels were significantly affected, regarding their microstructure and surface area. In general, an improvement of the removal efficiency after functionalization of aerogels with amine groups was found, with removal efficiencies higher than 90% for lead and Rubi Levafix CA. To explain the adsorption mechanism, both Langmuir and Freundlich models were applied; chemisorption is most likely the sorption type taking place in the studied cases.

Mechanical milling: a sustainable route to induce structural transformations in MoS2 for applications in the treatment of contaminated water

Two-dimensional (2D) nanomaterials have received much attention in recent years, because of their unusual properties associated with their ultra-thin thickness and 2D morphology. Besides graphene, a new 2D material, molybdenum disulfide (MoS₂), has attracted immense interest in various applications. On the other hand, ball-milling process provides an original strategy to modify materials at the nanometer scale. This methodology represents a smart solution for the fabrication of MoS₂ nanopowders extremely-efficient in adsorbing water contaminants in aqueous solution. This work reports a comprehensive morphological, structural, and physicochemical investigation of MoS₂ nanopowders treated with dry ball-milling. The adsorption performances of the produced nanopowders were tested using methylene blue (MB) dye and phenol in aqueous solution. The adsorption capacity as a function of ball-milling time was deeply studied and explained. Importantly, the ball-milled MoS₂ nanopowders can be easily and efficiently regenerated without compromising their adsorption capacity, so to be reusable for dye adsorption. The eventual toxic effects of the prepared materials on microcrustacean Artemia salina were also studied. The present results demonstrate that ball-milling of MoS₂ offers a valid method for large-scale production of extremely efficient adsorbent for the decontamination of wastewaters from several pollutants.

Removal of chromium(vi) from polluted wastewater by chemical modification of silica gel with 4-acetyl-3-hydroxyaniline

In the current study, a new adsorbent that is insoluble in water and many acid solutions and has a high adsorption capacity for Cr(vi) metal ions was synthesized. In the synthesis process, 3-chloropropyl-trimethoxysilane (CPTS) was first modified on a silica gel (Si) surface. Secondly, 4-acetyl-3-hydroxyaniline (AHAP) was immobilized on the modified silica gel compound (Si-CPTS). As a result of the immobilization process, a new adsorbent compound named Si-CPTS-AHAP (silica gel-3-chloropropyltrimethoxy silane 4-acetyl-3-hydroxyaniline) was obtained, which was used to separate Cr(vi) ions from aqueous solution (K₂Cr₂O₇) and industrial wastewater. The material was characterized using scanning electron microscopy and Fourier-transform infrared spectroscopy. The amount of chromium adsorbed was detected by ultraviolet-visible spectroscopy. The adsorption was evaluated using batch methods. The effects of temperature, pH, concentration, adsorbent amount and interaction time on the adsorption of Si-CPTS-AHAP were also investigated. The adsorption of Cr(vi) ions on Si-CPTS-AHAP was investigated via adsorption kinetics, isotherm and thermodynamic studies. The value of the isotherm parameters and the highest adsorption yields were calculated from the Dubinin–Radushkevich, Freundlich and Langmuir isotherm equations. Thermodynamic features such as entropy (ΔS), enthalpy (ΔH) and free energy (ΔG) were also calculated from the experimental results. The experimental results showed that the best recoveries of Cr(vi) metal ions are under the conditions of 180 min (interaction time), 0.05 g (adsorbent amount) and 323.15 K (temperature) at pH 2. Si-CPTS-AHAP can be used for the removal of poisonous pollutants in wastewater.

Use of a newly synthesized Si-CPTS-AHAP adsorbent in the removal of Cr(vi) ions in wastewater treatment systems may potentially lead to low cost and highly efficient heavy metal removal.

Green and sustainable zero-waste conversion of water hyacinth (Eichhornia crassipes) into superior magnetic carbon composite adsorbents and supercapacitor electrodes

Our facile approach converts embarrassing weed to value-added products through environmentally friendly routes towards zero-waste scheme.