The adsorption aspect of Cu2+ and Zn2+ on MCM-41 and SDS-modified MCM-41

Adsorption of Co2+ and Cr3+ in Industrial Wastewater by Magnesium Silicate Nanomaterials

In this paper, two flower-like magnesium silicate nanomaterials were prepared. These and another two commercial magnesium silicate materials were characterized using a scanning electron microscope, the N2 adsorption-desorption method, and other methods. The structure-activity relationship between the adsorption performance of these four magnesium silicate materials and their specific surface area, pore size distribution, and pore structure was compared. The results showed that the 3-FMS modified by sodium dodecyl sulfonate (SDS) had the largest specific surface area and pore size, the best adsorption performance, and the largest experimental equilibrium adsorption capacity (qe,exp) for Co2+, reaching 190.01 mg/g, and Cr3+, reaching 208.89 mg/g. The adsorption behavior of the four materials for Co2+ and Cr3+ both fitted the pseudo-second-order kinetic model and Langmuir adsorption model, indicating that chemical monolayer uniform adsorption was the dominant adsorption process. Among them, the theoretical adsorption capacity (qm) of 3-FMS was the highest, reaching 207.62 mg/g for Co2+ and 230.85 mg/g for Cr3+. Through further research, it was found that the four materials mainly removed Co2+ and Cr3+ through electrostatic adsorption, surface metal ions (Mg2+), and acidic groups (-OH and -SO3H) exchanging with ions in solution. The adsorption performance of two self-made flower-like magnesium silicate materials for Co2+ and Cr3+ was superior to that of two commercial magnesium silicates.

Modified approaches to prepare nano-magnesium silicates with hierarchical pore structure and their performance towards adsorption of Cd2

A series of flower-like magnesium silicate samples with hierarchical pore were prepared by the solvothermal method under template-free conditions using sodium dodecyl sulfate as the modifier and ethanol-water as the solvent. These samples were characterized by various methods and were evaluated for the adsorption of heavy metal Cd2+. The results showed that the adding modifier did not change the crystal structure of the magnesium silicate samples. In the range of 2~80 nm, they still showed hierarchical pore distribution mainly composed of mesopores and macropores, which facilitates the rapid transport of adsorbent within the pore channel. Therefore, the adsorption of Cd2+ was greatly accelerated. Meanwhile, the larger specific surface area (as high as 553 m2/g) of these samples significantly increased the theoretical maximum adsorption amount of Cd2+ up to 295.3 mg/g due to more available adsorption sites. The adsorption dynamic behavior of the samples on Cd2+ was in accordance with the pseudo-second-order adsorption model, and their thermodynamic behavior follows the Langmuir adsorption model. The adsorption mechanism of the sample was proposed as electrostatic adsorption and exchange of metal ions and acidic groups on its surface with ions in solution. The obtained magnesium silicate materials are expected to remove heavy metals from wastewater.

Recent Progress of Microwave-Assisted Synthesis of Silica Materials

Microwaves are a source of energy of great interest for chemical synthesis. Among nanomaterials, few are as versatile as silica—it forms mesoporous materials and nanoparticles, it can be incorporated as shells or loaded in composites, it can also be functionalized. Despite the relevant properties of silica, and the advantages of the use of microwave as energy source, its use in silica-based materials is not frequent. We report herein a compilation of the research results published in the last 10 years of microwave assisted synthesis of silica based materials. This review includes examples of mesoporous materials for waste removal, catalysis, drug release, and gas adsorption applications, together with examples based in the optimization of the synthesis conditions. In the case of non-porous materials, examples of analytical applications, coating of metallic nanoparticles, and SiO_x-C materials have been collected.

Investigating the Heavy Metal Adsorption of Mesoporous Silica Materials Prepared by Microwave Synthesis

Mesoporous silica materials (MSMs) of the MCM-41 type were rapidly synthesized by microwave heating using silica fume as silica source and evaluated as adsorbents for the removal of Cu²⁺, Pb²⁺, and Cd²⁺ from aqueous solutions. The effects of microwave heating times on the pore structure of the resulting MSMs were investigated as well as the effects of different acids which were employed to adjust the solution pH during the synthesis. The obtained MCM-41 samples were characterized by nitrogen adsorption-desorption analyses, X-ray powder diffraction, and transmission electron microscopy. The results indicated that microwave heating method can significantly reduce the synthesis time of MCM-41 to 40 min. The MCM-41 prepared using citric acid (c-MCM-41(40)) possessed more ordered hexagonal mesostructure, higher pore volume, and pore diameter. We also explored the ability of c-MCM-41(40) for removing heavy metal ions (Cu²⁺, Pb²⁺, and Cd²⁺) from aqueous solution and evaluated the influence of pH on its adsorption capacity. In addition, the adsorption isotherms were fitted by Langmuir and Freundlich models, and the adsorption kinetics were assessed using pseudo-first-order and pseudo-second-order models. The intraparticle diffusion model was studied to understand the adsorption process and mechanism. The results confirmed that the as-synthesized adsorbent could efficiently remove the heavy metal ions from aqueous solution at pH range of 5-7. The adsorption isotherms obeyed the Langmuir model, and the maximum adsorption capacities of the adsorbent for Cu²⁺, Pb²⁺, and Cd²⁺ were 36.3, 58.5, and 32.3 mg/g, respectively. The kinetic data were well fitted to the pseudo-second-order model, and the results of intraparticle diffusion model showed complex chemical reaction might be involved during adsorption process.

Preparation of an ion imprinted functionalized mesoporous silica for rapid and specific absorption Cr(iii) ions in effluents

We developed an effective and selective method to remove Cr(iii) ions in acidic effluents.

Highly efficient alginate sodium encapsulated chlorpyrifos/copper(ii) Schiff base mesoporous silica sustained release system with pH and ion response for pesticide delivery

A highly efficient sustained released system (ALG–CH–Cu–MCM-41) was prepared. The as-synthesized system showed significant pH and ion responsive.