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Anode graphite was recovered from a spent lithium ion battery (LIB) and reutilized as a carbon precursor to obtain graphene-based materials. Characterization results revealed that impurities were removed from the obtained graphite powder by cleansing processes. The as-synthesized reduced graphene oxide (rGO) from the purified graphite (LIB-rGO) demonstrated excellent catalytic ozonation activity against organic pollutants removal. To probe potential catalytic active sites, LIB-rGOs with different defective levels but similar oxygen contents were synthesized. Catalytic ozonation tests revealed that a higher defective level resulted in a greater catalytic activity. Density functional theory (DFT) calculation further demonstrated that ozone molecules could spontaneously decompose into active oxygen species on graphene structural vacancies and edges, which consolidated the role of defective structure in catalytic ozonation activity. Meanwhile, we discovered the pollutant-structure-dependent behavior of dominant reactive oxygen species (ROS) with the aid of radical scavenging tests and electron paramagnetic resonance (EPR) spectra. For phenolic pollutants vulnerable to direct ozone attacking, superoxide radicals (O 2 − ) and singlet oxygen ( 1 O 2 ) were found to be responsible ROS, whereas hydroxyl radicals ( OH) were identified as the principle ROS for aliphatic organic pollutants destruction. This study not only put forward a possible way for reutilization of waste LIB anode, but also stepped further for investigating the catalytic ozonation mechanism towards the graphene-based materials including the active sites and the generation of ROS. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nitration treatment enhanced the activity of activated carbon in catalytic ozonation. [•] The amination modification enhanced the activity of activated carbon in catalytic ozonation. [•] Acid oxygenated groups play a positive role in catalytic ozonation of oxalic acid. [•] This provides a new choice to promote the activity of activated carbon in catalytic ozonation. [Copyright &y& Elsevier]

• Hierarchical sphere-like LMO perovskite hybrids were prepared for O 3 activation. • Oxygen vacancies (OV) and multi-valence Mn were the main Lewis acidic sites. • DFT studies revealed OV and multi-valence Mn as active sites for O 3 decomposition. • Generated reactive species, O 2 −, OH and 1O 2 , were possible for BTA degradation. La-based perovskites are catalytically active owing to the oxygen vacancies, redox metal centers of B sites and surface hydroxyl groups. Nevertheless, the insights into these active centers on environmental catalysis are still insufficient. In this study, hierarchical mixed oxides perovskite microspheres were synthesized for catalytic ozonation over oxalic acid and benzotriazole. LaMn 4 O x , with LaMnO 3-δ as the dominant crystal phase, demonstrated superior catalytic activity to Mn 2 O 3 and LaMnO 3 synthesized from citric acid sol-gel method. Temperature-programmed desorption of NH 3 (NH 3 -TPD) and pyridine-Fourier transform infrared spectroscopy (pyridine-FTIR) tests proved Lewis acid as the main acid type. Temperature-programmed reduction of H 2 (H 2 -TPR), O 2 -TPD and X-ray photoelectron spectroscopy (XPS) analysis indicated the presence of oxygen vacancies and mixed valences of Mn in the crystal structure facilitated the catalytic process. Moreover, the content of oxygen vacancy was calculated by iodometric titration method. With the aid of theoretical calculations, oxygen vacancies were found to exhibit a strong affinity toward ozone adsorption, where ozone molecules spontaneously dissociated into reactive oxygen species (ROS) such as O 2 − and 1O 2. The B site of Mn facilitated ozone decomposition by extending the O O bond of ozone due to the electron transfer from Mn3+/Mn4+ redox cycle. In-situ EPR and quenching tests confirmed the contribution of O 2 − and 1O 2 in benzotriazole degradation along with OH. This study stepped further to unveil the ozone adsorption/decomposition and ROS generation on nanoscale perovskite-based composites. [ABSTRACT FROM AUTHOR]

The recent thrust in utilizing g-C 3 N 4 as a metal-free photocatalyst has led to accelerated attention in environmental decontamination. Despite of enormous efforts paid on material modification, the overall efficiency is still limited, especially for decomposition of chemically stable contaminants and mineralization of organics. Here, we coupled bulk g-C 3 N 4 (GCN-T and GCN-D synthesized from thiourea and dicyandiamide, respectively) photocatalysis with ozonation for mineralization of oxalic acid (OA) and p -hydroxybenzoic acid (PHBA) under UV and visible-light irradiation. The compelling experiments confirmed that bulk g-C 3 N 4 could trigger a super synergy between photocatalysis and ozonation under visible light. The apparent rate constant of OA removal by Vis/O 3 /GCN-D was 20.6 times as great as the sum of that in Vis/GCN-D and ozonation. The TOC removal of PHBA by Vis/O 3 /GCN-D was 98.0%, which was about 39.3% higher than the sum of that in Vis/GCN-D and ozonation. The high conduction band (CB) position of g-C 3 N 4 proved to be crucial for the synergy between photocatalysis and ozonation. GCN-D possessed a ∼0.10 V upshifted CB level compared to GCN-T, resulting in a 1.30 times higher photocatalytic ozonation activity. More negative CB potential benefited photoinduced electron capture by ozone molecules, thus significantly enhanced charge separation as well as the decay of ozone eventually with generation of abundant hydroxyl radicals ( OH). Exceptionally, Vis/O 3 /GCN-D exhibited stronger oxidizing ability than UV/O 3 /GCN-D for OA degradation with the same light intensity. The reason was that the photolysis of ozone occurred under UV and partly inhibited ozone capturing photoinduced electrons. The amount of generated OH thus decreased in UV/O 3 /GCN-D instead with the formation of a few atomic oxygen species (O ( 1 D)). This study puts forward new application of the easily obtained bulk g-C 3 N 4 and may drive the advance of sunlight/O 3 /g-C 3 N 4 method for efficient and green water decontamination using sunlight as energy source. [ABSTRACT FROM AUTHOR]