Zhiyan Pan

1. Geological carbon sequestration (GCS) is a critical strategy for achieving global carbon neutrality by capturing and immobilising anthropogenic CO2 within deep subsurface reservoirs [1]. The con...

To achieve efficient removal and defluorination of perfluorooctanoic acid (PFOA), a visualized micro-scale fused quartz tube reactor (FQTR) was constructed to systematically investigate sub/supercritical water oxidation (SCWO) processes. Under operating conditions of 200–400 °C and 8–27.3 MPa, PFOA underwent rapid degradation with near-complete conversion. The incorporation of γ-MnO₂ markedly enhanced the PFOA degradation at low temperature and achieved faster fluorine removal. At the conditions of 300 °C, 40 min, O/C ratio (oxygen-to-carbon molar ratio) = 1.5, and pH = 7, the degradation and defluorination efficiencies increased by 12.56% and 15.21%, respectively, compared with the non-catalytic system. This enhancement is primarily attributed to the efficient activation of H₂O₂ by γ-MnO₂, which promotes the breaking of C–F bond and accelerates the converting of PFOA into CO₂ and fluoride ions. The SEM, Raman and leaching experiment results demonstrated that γ-MnO₂ exhibits excellent structural stability and reusability. Furthermore, density functional theory (DFT) calculations were performed to identify potential reactive sites and elucidate degradation pathways at the molecular level, providing mechanistic support for the experimental observations. Overall, the γ-MnO₂-catalyzed SCWO exhibits excellent degradation and defluorination performance for PFOA removal, providing useful insight into the treatment of fluorinated wastewater.

Conventional wastewater biological nitrogen removal (BNR) processes require a large amount of air and external organic carbon, causing a significant increase in operating costs and potential secondary pollution. Herein, this study investigated the nitrogen removal performance and the underlying mechanisms of a novel simultaneous nitrification and denitrification (SND) coupled with photoautotrophic assimilation system in an inversed fluidized bed bioreactor (IFBBR). Nitrogen removal was achieved through the synergistic interaction of microalgae and bacteria, with microalgae providing O₂ for nitrification and microbial biomass decay supplying organic carbon for denitrification. The IFBBR was continuously operated for more than 240 days without aeration and external organic carbon, the total nitrogen (TN) removal efficiency reached over 95%. A novel C-N-O dynamic balance model was constructed, revealing that nitrification and denitrification were the primary pathways for nitrogen removal. The model further quantified the microbial contributions, showing that microalgae generated O₂ at a rate of 81.82 mg/L·d, while microbial biomass decay released organic carbon at a rate of 148.66 mg/L·d. Microbial diversity analysis confirmed the majority presence of microalgae (Trebouxiophyceae), nitrifying bacteria (Gordonia and Nitrosomonas) and denitrifying bacteria (Ignavibacterium and Limnobacter). This study successfully achieved enhanced nitrogen removal without the need for aeration or external organic carbon. These advancements provide valuable insights into efficient wastewater nitrogen removal, offering significant benefits in terms of reduced energy consumption, lower operational costs, and decreased CO₂ emissions.

Catalysis involving gold supported on metal oxides has undergone extensive examination. However, the nature of the catalytic site under actual reaction conditions and the role of the support continue to be vigorously debated. This study addresses these issues through experimental investigations and theoretical simulations. We explore a novel catalytic mechanism that employs dynamic single-atom catalysis for the hydrochlorination of acetylene. This catalytic mechanism occurs in defective ZrO₂-supported Au-Zr single-atom alloys. Specifically, the dynamic single-atom catalysis is a result of the mobility of the gold cation, which is accelerated by Cl radicals and strongly couples with the abundant unsaturated surface sites of ZrO₂ in a synergistic manner. As a result, the Au electronic structure dynamically evolves, leading to a decrease in the addition reaction energy barrier. Notably, the Au cation can detach from the Au-Zr alloy structure to catalyze the hydrochlorination of acetylene near the Zr-O_v-Zr sites and then reintegrate back into the Au-Zr alloy structure upon completion of the reaction. This study underscores the significance of dynamic active sites under reaction conditions and their pivotal role in catalysis.

Understanding the solubility of CO₂ is critical for implementing CO₂-enhanced oil recovery (CO₂-EOR). In this work, the solubility of CO₂ in n-decane in a temperature range between 303.15 K and 353.15 K and pressures up to 15 MPa was measured using a fused silica capillary cell with in situ Raman spectroscopy. A semi-empirical CO₂ solubility prediction model was obtained according to the experimental results. In order to improve the solubility of CO₂ in n-decane, the solubility of CO₂ in n-decane and co-solvent n-hexane (3% wt) mixture was also comparatively investigated. The results indicated that the solubility of CO₂ in n-decane was 1.6355~64.0084 mol/kg. The data from the prediction model were in good agreement with the experimental data, and the mean relative deviation was 3.65%, indicating that the prediction model could be used to predict the solubility of CO₂ in n-decane under different conditions. The solubility of CO₂ in n-decane + n-hexane system ranged from 1.0127 mol/kg to 65.7286 mol/kg. It was found that, under low-pressure conditions, the addition of co-solvent n-hexane did not enhance the solubility of CO₂, while it had a certain enhancement effect on the dissolution of CO₂ under high-pressure conditions. As the temperature increased from 303.15 K to 353.15 K, the enhancement efficiency of the solubility of CO₂ also increased from 1.34~2.05% to 8.17~9.82%, and the average enhancement efficiency increased from 1.74% to 9.00%. This study provides more CO₂ solubility data for CO₂-EOR.