Zhujian Huang

This study presents a novel green approach for the preparation of zeolite material from fly ash using a combination of mechanochemical methods. The physicochemical properties of the synthesized zeolite, including crystal structure and porosity, were systematically investigated. The synthesized zeolite was employed for the adsorption of ammonia nitrogen from aqueous solutions, and their adsorption kinetics and thermodynamics were comprehensively studied. The results revealed that the adsorption of ammonia nitrogen onto the zeolite follows the Langmuir adsorption model. Additionally, the zeolite exhibited strong selective adsorption and remarkable resistance to interference from coexisting cations in the aqueous solution. Finally, regeneration experiments were conducted using NaCl, NaClO, and their mixtures to desorb ammonia nitrogen from the spent zeolite. A total of 17 regeneration cycles were performed until the adsorption capacity of the zeolites was exhausted. The adsorption performance of the regenerated zeolite was evaluated to assess the impact of different reagents and regeneration cycles on adsorption efficiency. The optimal regeneration method was identified, leading to the successful valorization of fly ash into zeolite for ammonia adsorption and the development of effective regeneration strategies for spent zeolite.

In recent years, the excessive use and improper disposal of antibiotics have led to their pervasive presence in the environment, resulting in significant antibiotic pollution. To address this pressing issue, the present study synthesized nickel–iron-layered double hydroxides (NiFe-LDHs) with varying molar ratios using a hydrothermal method, employing these LDHs as catalysts for the oxidative degradation of doxycycline, with peroxymonosulfate (PMS) serving as the oxidant. X-ray diffraction analysis confirmed that the synthesized NiFe-LDHs exhibited a hexagonal crystal structure characteristic of layered double hydroxides. Experimental results demonstrated that the catalytic efficiency of NiFe-LDHs increased with both the dosage of the catalyst and the concentration of PMS, achieving a high degradation efficiency for doxycycline at a catalyst concentration of 0.5 g/L. Furthermore, the catalytic performance was notably effective across a range of pH conditions, with the highest degradation efficiency being observed at a Ni–Fe molar ratio of 3:1. The activation of PMS by NiFe-LDHs for the catalytic degradation of pollutants primarily occurs through singlet oxygen (¹O₂), superoxide radicals (O₂⁻·), and sulfate radicals (SO₄⁻·). The study also proposed three potential degradation pathways for doxycycline, indicating that the final degradation products have lower environmental toxicity. This research offers novel approaches and methodologies for the treatment of antibiotic-contaminated wastewater.

This study presents a novel green approach for the preparation of zeolite material from fly ash using a combination of mechanochemical method. Compared to traditional methods, this approach reduces energy consumption, minimizes reagent usage, and facilitates the efficient recycling of fly ash. The physicochemical properties of the synthesized zeolite, including crystal structure and porosity, were systematically investigated. The synthesized zeolite was employed for the adsorption of ammonia nitrogen from aqueous solutions, and their adsorption kinetics and thermodynamics were comprehensively studied. The results revealed that the adsorption of ammonia nitrogen onto the zeolite follows the Langmuir adsorption model. Additionally, the zeolite exhibited strong selective adsorption and remarkable resistance to interference from coexisting cations in the aqueous solution. Finally, regeneration experiments were conducted using NaCl, NaClO, and their mixtures to desorb ammonia nitrogen from the spent zeolite. A total of 17 regeneration cycles were performed until the adsorption capacity of the zeolites was exhausted. The adsorption performance of the regenerated zeolite was evaluated to assess the impact of different reagents and regeneration cycles on adsorption efficiency. The optimal regeneration method was identified, leading to the successful valorization of fly ash into zeolite for ammonia adsorption and the development of effective regeneration strategies for spent zeolite.

Non-free radical photocatalysis with metal oxide catalysts is an important advanced oxidation process that enables the removal of various emerging environmental pollutants, such as tetracycline. Here, four hexagonal La₂O₃ photocatalysts with different densities of oxygen vacancy and crystalline features are synthesized and then further treated by ball milling. Ball milling of these La₂O₃ photocatalysts is found to increase the amount of oxygen vacancies on their surfaces and thereby the amount of ¹O₂ species produced by them. The photocatalytic degradation of TC by these La₂O₃ photocatalysts depends on the oxygen vacancies present on them. Furthermore, the ones with a strong (101) diffraction peak remove tetracycline from water systems largely with ¹O₂ and ^•OH species, whereas those with a weak (101) diffraction peak do so mainly via ¹O₂ and direct electron transfer (DET) process. Their overall catalytic properties are also studied by density functional theory calculations. Moreover, the organic products produced from tetracycline by La₂O₃ photocatalysts containing a strong (101) diffraction peak are found to be less toxic than those produced by La₂O₃ photocatalysts containing a weak (101) diffraction peak. This study also provides convincing evidence that the structures of La₂O₃ determine the species that is produced by it and that end up mediating photocatalytic reaction pathways (i.e., free radical versus non-free radical) to degrade an emerging environment pollutant.