Hebei Messi Biology Co., Ltd. stated that with the rapid development of the national economy and the increasing awareness of environmental protection, sewage treatment has not only become the focus and difficulty of China’s comprehensive water environment improvement, but also directly related to people’s health and national sustainable development. Among many treatment methods, adsorption has been widely used due to its advantages of simple operation, low cost and environmental friendliness. Its treatment effect (treatment capacity and treatment speed) mainly depends on the chemical composition and pore structure of the adsorbent material. Therefore, the controllable preparation of high-efficiency and low-cost adsorbent materials and their adsorption behavior research are of great significance and practical application value for China’s efficient sewage treatment.
In comparison, magnesium oxide adsorption materials have the advantages of abundant sources, low cost and rich surface active sites. They have been applied in the treatment of printing and dyeing industrial wastewater, heavy metal wastewater and domestic sewage. However, they have disadvantages such as low specific surface area and wide pore size distribution, which greatly limits the performance of their adsorption efficiency. Based on the acid-base duality and ammonia slow-release characteristics of aluminum hydroxide, the pore structure of magnesium oxide adsorbent is regulated by regulating the release of ammonia during the formation of magnesium oxide precursor magnesium carbonate and utilizing the dissolution mechanism of aluminum hydroxide generated at low pH under high pH conditions; using organic dye methyl orange (MO) and heavy metal lead ion (Pb2+) as probes, the influence of the pore structure of magnesium oxide adsorbent on the adsorption performance of the two is discussed in detail, thereby revealing the structure-activity relationship between the pore structure and adsorption performance of magnesium oxide, and providing a scientific basis for the pore structure design and controllable preparation of high-efficiency magnesium oxide adsorbent. The contents and results are as follows:
(1) Using magnesium chloride as the magnesium source and urea as the ammonia slow-release precipitant, a cubic magnesium carbonate precursor is prepared by hydrothermal method, and a high specific surface area cubic magnesium oxide adsorbent is prepared by calcination in air atmosphere, and its adsorption performance for MO is systematically discussed. The research results show that the specific surface area of the prepared adsorbent material is 182m2/g, and the average pore size is between 6 and 8nm; the adsorption behavior of the adsorbent material for methyl orange follows the pseudo-second-order kinetic equation and the Freundlich adsorption isotherm equation, and the adsorption equilibrium is reached in about 10min. The maximum equilibrium adsorption amount is above 3000mg/g, and it has excellent adsorption performance.
(2) Using magnesium chloride and aluminum chloride as magnesium source and aluminum source, urea as ammonia slow-release precipitant and aluminum hydroxide template dissolving agent, the magnesium carbonate precursor was prepared by hydrothermal method (180℃), and then calcined at 550℃ in air atmosphere to form a straight-through mesoporous magnesium oxide adsorption material, and the adsorption behavior and mechanism of the adsorbent material for MO and Pb2+ were studied. The research results show that by adjusting the ratio of magnesium to aluminum, wheat-ear-shaped magnesium oxide with high specific surface area and rich through-pore structure can be prepared; the specific surface area of the adsorbent material can reach 136m2/g, and the average pore size is between 5 and 8nm; the adsorption process of methyl orange and lead ions by the adsorbent material follows the quasi-second-order kinetic equation and the Langmuir adsorption isotherm equation, and the maximum adsorption capacity of methyl orange is 5483mg/g, and the maximum adsorption capacity of lead ions is 2359mg/g.
(3) Using magnesium chloride and aluminum chloride as magnesium and aluminum sources, urea as ammonia slow-release precipitant, and surfactants hexadecyltrimethylammonium bromide (CTAB) and hexadecyltrimethylammonium chloride (CTAC) as morphology control agents, two wheat-ear-shaped magnesium oxide adsorbent materials can be prepared by hydrothermal method and calcination method, and their adsorption performance for methyl orange is investigated in detail. The research results show that the introduction of surfactants has no significant effect on the morphology of the adsorption material; after adding CTAB, the specific surface area of the wheat-ear-shaped magnesium oxide increased to 171m2/g, and the average pore size was 6.31nm. The adsorption process of methyl orange by the adsorption material follows the quasi-second-order kinetic equation and the Freundlich adsorption isotherm equation, the equilibrium time is shortened to 10min, and the maximum equilibrium adsorption capacity is 3353mg/g; after adding CTAC, the specific surface area of the wheat-ear-shaped magnesium oxide increased to 166m2/g, and the average pore size was 5.55nm. The adsorption process of methyl orange by the adsorption material follows the quasi-second-order kinetic equation and the Langmuir adsorption isotherm equation, the equilibrium time is shortened to 10min, and the maximum equilibrium adsorption capacity is 3518mg/g.