Stable O3 Decomposition by Layered Double Hydroxides: The Pivotal Role of NiOOH Transformation.

Because ozone (O3) is a significant air pollutant, advanced O3 elimination technologies, particularly those under high-humidity conditions, have become an essential research focus. In this study, a nickel-iron layered double hydroxide (NiFe-LDH) was modified via intercalation with octanoate to develop an effective hydrophobic catalyst (NiFe-OAa-LDH) for O3 decomposition. The NiFe-OAa-LDH catalyst sustained its O3 decomposition rate of >98% for 48 h under conditions of 90% relative humidity, 840 L/(g·h) space velocity, and 100 ppm inlet O3 concentration. Moreover, it maintained a decomposition rate of 90% even when tested at a higher airflow rate of 2500 L/(g·h). Based on the changes induced by the Ni-OII to Ni-OIII bonds in NiFe-OAa-LDH during O3 treatment, catalytic O3 decomposition was proposed to occur in two stages. The first stage involved the reaction between the hydroxyl groups and O3, leading to the breakage of the O-H bonds, formation of NiOOH, and structural changes in the catalyst. This transformation resulted in the formation of abundant and stable hydrogen vacancies. According to density functional theory calculations, O3 can be effectively decomposed at the hydrogen vacancies with a low energy barrier during the second stage. This study provides new insights into O3 decomposition.

Enhanced NOx absorption in flue gas by wet oxidation of red mud and phosphorus sludge.

The environmental problem caused by industrial emissions of NOx has been studied in the past dacades. In this study, red mud coupling with phosphorus sludge were used to enhance the solution to absorb NOx from the flue gas. Firstly, red mud reacted with the binder silicic acid in the phosphorus sludge, destroying the emulsion structure of the phosphorus sludge. Then, the P4 in the phosphorus sludge is completely released, and the P4 reacted with O2 in the flue gas to produce O3 and O. NO and NO2 contained in the flue gas reacted with the active O and O3 to produce high-valent NOx, such as NO3, N2O5. At last, the mixed slurry of red mud and phosphorus sludge absorbed the high-valent NOx, resulting in the formation of Ca5(PO4)3F along with HNO3. Using phosphorus sludge to produce O3 in the reaction process can reduce the production cost of O3 and achieve waste utilization. Meanwhile, the interaction between red mud and phosphorus sludge can promote phosphorus sludge to produce O3 and remove F- from phosphorus sludge, as well as avoid the problem of secondary pollution. This study should be helpful for red mud and phosphorus sludge utilization and flue gas denitration.

Catalytic degradation of antibiotic sludge to produce formic acid by acidified red mud.

As complex and difficult-to-degrade persistent organic pollutants (POPs), antibiotics have caous damage to the ecological enused serivironment. Because of the difficult degradation of antibiotics, sewage and sludge discharged by hospitals and pharmaceutical enterprises often contain a large number of antibiotic residues. Therefore, the harmless and resourceful treatment of antibiotic sludge is very meaningful. In this paper, amoxicillin was selected as a model compound for antibiotic sludge. Acidified red mud (ARM) was used to degrade antibiotic sludge and produce hydrogen energy carrier formic acid in catalytic wet peroxidation system (CWPO). Based on various characterization analyses, the reaction catalytic mechanism was demonstrated to be the result of the non-homogeneous Fanton reaction interaction between Fe3O4 on the ARM surface and H2O2 in solution. Formic acid is the product of the decarboxylation reaction of amoxicillin and its degradation of various organic acids. The formic acid was produced up to 792.38 mg L-1, under the optimal conditions of reaction temperature of 90 °C, reaction time of 30 min, H2O2 concentration of 20 mL L-1, ARM addition of 0.8 g L-1, pH = 7, and rotor speed of 500 rpm. This research aims to provide some references for promoting red mud utilization in antibiotic sludge degradation.

Enhanced sequestration of CO2 from simulated electrolytic aluminum flue gas by modified red mud.

The aluminum industry is facing severe economic and environmental problems due to increasing carbon emissions and growing stockpiles of red mud (RM). RM is a strongly alkaline, high-emission solid waste from the alumina industry with potential for CO2 sequestration. However, the effectiveness of RM carbon sequestration is poor, and the mechanism behind it is not well understood. In this study, the effect of microwave and tube furnace activation of RM on CO2 sequestration in alumina was first investigated at different temperatures. The result showed that the CO2 sequestration capacity of unmodified RM (URM) was only 14.35 mg/g at ambient temperature and pressure, and the CO2 sequestration capacity could be increased to 52.89 mg/g after high-temperature activation and modification. Besides, high-temperature activation and modification will effectively improve the carbon sequestration capacity of RM. The carbonized RM was characterized by FT-IR, SEM, XRD, laser particle size, TG-DSC, and pH measurements. In addition, the mechanism of RM capturing CO2 was also proposed, which shows that CO2 was finally sequestered in the RM as CaCO3. The change in particle size distribution and the mineral phase in the RM indicated that high-temperature activation modification positively affects the application of RM to the sequestration of CO2. This study can provide a promising technology for the low-carbon and green development of the aluminum industry, as well as achieving the waste treatment and utilization objective.

Resource degradation of pharmacy sludge in sub-supercritical system with high degradation rate of 99% and formic acid yield of 32.44.

In response to the social goal of 'carbon peak and carbon neutral' in the 14th Five-Year Plan of China, this article used Enrofloxacin (ENR), a common antibiotic, as a model compound to study the method of efficiently degrading pharmaceutical sludge and simultaneously producing Formic Acid (FA), hydrogen storage energy, in a sub-supercritical system. The Ni/SnO2 bimetallic catalyst, which was prepared by the equal volume impregnation method, was used for the liquid phase catalysis. As shown by the results, when the reaction temperature was 330°C, and the addition amount of H2O2 was 0.38 mL, the degradation rate of antibiotics could reach 99% after the reaction proceeded for 6 h. In terms of the resource utilization, the yield of FA could reach up to 32.44%. The resource utilization efficiency with Ni/SnO2 catalyst in sub-/supercritical reaction was about 2.5 times higher than that without catalyst. The kinetic reaction model was established to explore the reaction rate of the antibiotic degradation process. In addition, the Ea and the frequency factor of the reaction were 6455 J/mol and 5.78, respectively. As shown by characterization, the prepared Ni/SnO2 bimetallic catalyst had good activity and has already passed repeated stability experiments. In short, this method has broad application prospects in antibiotic catalysis and resource degradation.