Preparation of Uniform Highly Dispersed Mg–Al-LDHs and Their Adsorption Performance for Chloride Ions

Preparation of acid-modified waste mask-based activated carbon grafted chitosan composites and their efficient removal of uranyl ions

Resource utilization of waste masks is of great significance for environmental protection. In this study, acid-modified waste mask-based activated carbon grafted chitosan composites (CSMA) were prepared using waste masks as a carbon source, chemically modified by introducing sulphonic acid groups through sulfuric acid treatment and further loaded with chitosan, and used for the efficient removal of U(VI) from aqueous solutions. Various characterization techniques, including SEM, FTIR, BET, and XPS, were utilized to investigate the microstructure and surface chemistry of CSMA. The experimental data indicate that optimal adsorption efficiency for CSMA about U(VI) is achieved at a pH of 7, utilizing an adsorbent dosage(m/V) of 0.1 g·L-1, a reaction duration of 6 h, and a temperature of 303 K. Under these conditions, the maximum adsorption capacity reaches 467.93 mg/g. From the kinetic and thermodynamic results of adsorption, it can be seen that the process of CSMA adsorption on uranyl ions was more in line with the Langmuir isotherm model and pseudo-second-order model. Thermodynamic analysis further confirms that this adsorption process is spontaneous and endothermic. In complex aqueous environments containing various co-existing ions, CSMA demonstrates good selective adsorption capabilities. After several testing cycles, CSMA still maintains a high adsorption efficiency for U(VI). Mechanistic studies using XPS/FTIR suggested that U(VI) capture was governed by coordination/chelation with surface functional groups (-NH2, -OH, -SO3H). This study not only presents an innovative approach for resource utilization from discarded masks but also offers an efficient and cost-effective solution for removing radioactive nuclides and facilitating environmental remediation.

Preparation of phosphoric-modified aloe vera/chitosan aerogels and their efficient adsorption of U(VI)

The efficient adsorption of radioactive elements from nuclear wastewater is an important research topic in the environmental field. The unique three-dimensional porous structure of aerogels has great potential in the field of adsorption. Phosphoric-modified aloe vera/chitosan aerogel (CS/AL-AP) was prepared from chitosan, phosphoric acid, and aloe powder by vacuum freeze-drying self-assembly. The maximum adsorption of uranyl ions by CS/AL-AP was found to be 322.34 mg/g at pH 6, adsorption time of 120 min, solid-to-liquid ratio of 0.125 g/L, reaction temperature of 303 K, and initial uranyl ion concentration of 50 mg/L. The adsorption process is consistent with the Langmuir isotherm model and the quasi-secondary kinetic model, indicating that the adsorption process is monolayer adsorption. The type of adsorption is mainly chemisorption. FTIR and XPS analyses indicate that the adsorption of U(VI) by CS/AL-AP results from the combined action of coordination or chelation of amino, hydroxyl, and carboxyl groups. In addition, CS/AL-AP shows excellent adsorption capacity in the presence of complex co-existing ions. After five adsorption-desorption experiments, the adsorption capacity of CS/AL-AP for uranyl ions remained at a high level. It indicates that CS/AL-AP has good stability and recoverability. The results indicate that CS/AL-AP has excellent potential in the field of uranium removal.

Use of catalytic wet air oxidation (CWAO) for pretreatment of high-salinity high-organic wastewater

Catalytic wet air oxidation (CWAO) coupled desalination technology provides a possibility for the effective and economic degradation of high salinity and high organic wastewater. Chloride widely occurs in natural and wastewaters, and its high content jeopardizes the efficacy of Advanced oxidation process (AOPs). Thus, a novel chlorine ion resistant catalyst B-site Ru doped LaFe_1-xRu_xO_3-δ in CWAO treatment of chlorine ion wastewater was examined. Especially, LaFe_0.85Ru_0.15O_3-δ was 45.5% better than that of the 6%RuO₂@TiO₂ (commercial carrier) on total organic carbon (TOC) removal. Also, doped catalysts LaFe_1-xRu_xO_3-δ showed better activity than supported catalysts RuO₂@LaFeO₃ and RuO₂@TiO₂ with the same Ru content. Moreover, LaFe_0.85Ru_0.15O_3-δ has novel chlorine ion resistance no matter the concentration of Cl^- and no Ru dissolves after the reaction. X-ray diffraction (XRD) refinement, X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), and X-ray absorption fine structure (XAFS) measurements verified the structure of LaFe_0.85Ru_0.15O_3-δ. Kinetic data and density functional theory (DFT) proved that Fe is the site of acetic acid oxidation and adsorption of chloride ions. The existence of Fe in LaFe_0.85Ru_0.15O_3-δ could adsorb chlorine ion (catalytic activity inhibitor), which can protect the Ru site and other active oxygen species to exert catalytic activity. This work is essential for the development of chloride-resistant catalyst in CWAO.

Preparation of ZnNiAl-LDHs microspheres and their adsorption behavior and mechanism on U(VI)

Ternary zinc-nickel-aluminum hydrotalcites (ZnNiAl-LDHs) were prepared by hydrothermal synthesis. The structure and morphology of the materials were characterized using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), nitrogen adsorption-desorption (BET) and other test techniques. ZnNiAl-LDHs was applied in the treatment of uranium-containing wastewater, the effects of initial pH of the solution, adsorption temperature and contact time on its adsorption performance were systematically investigated, and the adsorption performance of ZnNiAl-LDHs and ZnAl-LDHs on uranyl ions were compared. The result showed that ZnNiAl-LDHs were 3D microspheres self-assembled from flakes, with a specific surface area of 102.02 m²/g, which was much larger than that of flake ZnAl-LDHs (18.49 m²/g), and the saturation adsorption capacity of ZnNiAl-LDHs for uranyl ions (278.26 mg/g) was much higher than that of ZnAl-LDHs for uranyl ions (189.16 mg/g), so the ternary ZnNiAl-LDHs had a more excellent adsorption capacity. In addition, kinetic and thermodynamic studies showed that the adsorption process of ZnNiAl-LDHs on uranyl ions conformed to the pseudo-second-order kinetic model and Langmuir isotherm model. The positive value of ΔH and the negative value of ΔG indicated that the adsorption process was endothermic and spontaneous. The adsorption mechanism was analyzed by X-ray energy spectroscopy (EDS), fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The results showed that the adsorption of uranyl ions by ZnNiAl-LDHs mainly consisted of complexation and ion substitution. The research results prove that ZnNiAl-LDHs is an adsorbent with low cost and excellent performance, and it has a good application prospect in the field of uranium-containing wastewater treatment.

Super-stable mineralization effect of layered double hydroxides for heavy metals: Application in soil remediation and perspective

Agriculture soil plays a crucial role in sustainable development of human society. Unfortunately, soil quality is continuing degradation due to industrial and agricultural activities. Among them, agriculture soil contamination by heavy metals has become a serious threat to global food safety and human health. Because of low-cost, easy to implement, and fast effects, in situ chemical stabilization strategy has drawn great attention in soil remediation fields. However, since heavy metals are not removed from soil, it is still a great challenge to develop the cost-effective stabilizers with strong and long-term immobilization ability. Layered double hydroxides (LDHs) have been extensively applied in environmental fields owing to their unique structure. Very recently, LDHs have been used as amendment in in situ soil remediation for immobilization of heavy metals, exhibiting excellent long-term stability in practice application through trapping heavy metal ions into the lattice of LDHs layer. Given that the super-stable mineralization effect of LDHs for heavy metals, we summarize the structure of LDHs, key points of super-stable mineralization, practical challenges, and potential applications in other heavy metals pollution scenarios in this article, wishing that could provide new strategies and insights into rational designing of amendments for soil remediation.