Hierarchically porous SiO2/C hollow microspheres: a highly efficient adsorbent for Congo Red removal

Green and Facile Synthesis of Porous SiO2@C Adsorbents from Rice Husk: Preparation, Characterization, and Their Application in Removal of Reactive Red 120 in Aqueous Solution

In this work, a green, novel, fast, and facile approach for synthesizing a SiO2/C nanocomposite series from rice husk (RH) through quenching and grinding techniques has been reported along with its application for the adsorptive removal of Reactive Red 120 (RR120) dye from an aqueous solution. The effect of carbonization temperature on the textural and interfacial features of RH was confirmed by scanning electron microscopy (SEM), while the structure and elemental composition of the as-synthesized RH were investigated via XRD, Brunauer-Emmett-Teller (BET), FT-IR, Raman, and X-ray photoelectron spectroscopy (XPS). The RH had a high surface area (521.35 m2 g-1), large micropores, mesopores, and total pore volumes of 0.5059, 3.9931, and 5.2196 cm3 g-1, while SiO2 and C were the two major components. In the batch adsorption test, the effects of pH, contact time, adsorbent mass, temperature, and initial RR120 concentration were investigated. The maximum adsorption capacity was fitted by Langmuir, Freundlich, Temkin, Dubinin-Radushkevich (D-R), Hasley, Harkins-Jura, and BET isotherm models, and Langmuir was the best-fitted model. In addition, the pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich chemisorption models were used to explain the adsorption kinetics. Additionally, the values of Gibbs free energy, enthalpy, and entropy thermodynamics suggested that the RR120 adsorption phenomenon by RH8-3 was endothermic and spontaneous. The adsorption process was controlled by a physical mechanism, and the maximum adsorption capacity was found to be 151.52 mg g-1 at pH 2, with a contact time of 90 min, adsorbent amount of 0.03 g, and temperature of 313 K. The adopted technique may open up a new alternative route for the mass utilization of RH for the removal of dyes in water and wastewater and also for various practical applications.

Facile green synthesis of ZnO-CdWO4 nanoparticles and their potential as adsorbents to remove organic dye

In this work, ZnO-CdWO₄ nanoparticles have been synthesized by the ecofriendly green method with lemon leaf extract to favorably anchor functional groups on their surface. The prepared ZnO-CdWO₄ nanoparticles are used as adsorbent to treat Congo red (CR) dye after characterization through FT-IR, UV-Vis, TEM, SEM-EDX, and HRTEM techniques. The equilibrium partition coefficient and adsorption capacity values for CR by ZnO-CdWO₄ are estimated as 21.4 mg g^-1 μM^-1 and 5 mg g^-1, respectively (at an initial dye concentration of 10 mg L^-1). The adsorption process is found as exothermic and spontaneous, as determined by the ΔG°, ΔS°, and ΔH° values. The Boyd plot has been used as a confirmatory tool to fit the adsorption kinetics data along with intraparticle diffusion and pseudo-second-order models. Based on this research, ZnO-CdWO₄ nanoparticles are validated as an effective adsorbent for CR dye in aqueous solutions.

The synergetic effect of a structure-engineered mesoporous SiO2–ZnO composite for doxycycline adsorption

The design and synthesis of an efficient adsorbent for antibiotics-based pollutants is challenging due to the unique physicochemical properties of antibiotics. The development of a mesoporous SiO₂–ZnO composite is a novel way to achieve excellent adsorption efficiency for doxycycline hydrochloride (DOX) in aqueous solutions due to the engineered highly open mesoporous structure and the ZnO-modified framework. Unlike the traditional method of obtaining mesoporous composites by post-synthesis techniques, the novel one-step method developed in this study is both effective and environment-friendly. The adsorption mechanism based on the novel synergetic effect between SiO₂ and ZnO was demonstrated through several experiments. SiO₂ led to the creation of a 3D open framework structure that provides sufficient space and rapid transport channels for adsorption, ensuring rapid adsorption kinetics. A higher number of active sites and enhanced affinity of the contaminants are provided by ZnO, ensuring high adsorption capacity. The mesoporous SiO₂–ZnO could be easily regenerated without a significant decrease in its adsorption efficiency. These results indicate that the developed strategy afforded a simple approach for synthesizing the novel mesoporous composites, and that mesoporous SiO₂–ZnO is a possible alternative adsorbent for the removal of DOX from wastewater.

The design and synthesis of an efficient adsorbent for antibiotics-based pollutants is challenging due to the unique physicochemical properties of antibiotics.

Three hierarchical porous magnesium borate microspheres: a serial preparation strategy, growth mechanism and excellent adsorption behavior for Congo red

The 3D hierarchical porous 7MgO·2B₂O₃·7H₂O (MBH) microspheres were prepared by a phase transformation of chloropinnoite firstly, and anhydrous α-3MgO·B₂O₃ (MBA) microspheres were obtained by thermal conversion of 7MgO·2B₂O₃·7H₂O, and then β-3MgO·B₂O₃ (MBB) microspheres were obtained by phase conversion of α-3MgO·B₂O₃. All samples were characterized by XRD, FT-IR, TG and SEM. The microsphere nanostructures with a hierarchical porous structure were assembled by nanosheets with a thickness of 20–30 nm, and the growth mechanisms were also proposed. By using N₂ adsorption–desorption, the specific surface areas were measured as 103.62 m² g⁻¹ for MBH and 46.10 m² g⁻¹ for MBA. They exhibited excellent selective adsorption performance for Congo red (CR) with maximum adsorption capacities of 202.84 and 170.07 mg g⁻¹ respectively, and the corresponding adsorption mechanisms were also investigated. The adsorption processes were well fitted with the pseudo-second-order rate equation and Langmuir adsorption model. In addition, the corresponding adsorption thermodynamic parameters were also calculated. It is necessary to highlight that the hierarchical porous microspheres could be considered as promising candidates for removal of CR dye pollutants.

Three 3D hierarchical porous 7MgO·2B₂O₃·7H₂O and 3MgO·B₂O₃ microspheres assembled by nanosheets have been prepared by a serial preparation strategy. They exhibited excellent selective adsorption performance for Congo red with high adsorption capacities.