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Three simple structured nitrogen heterocyclic compounds (NHCs), namely indole (ID), benzopyrazole (BP) and benzotriazole (BT), were degraded via wet air oxidation (WAO) in an autoclave-type reactor. The elimination of target pollutants became significant only above 220 °C. The reactivity order of the three substrates was ID > BP > BT. The chemical oxygen demand (COD) removal levels were lower than 70%. Many partial oxidation intermediates were produced, as detected by electrospray ionization–mass spectrometry (ESI-MS). The presence of different anions, such as CO 3 2− , SO 4 2− , and PO 4 3− , had a detrimental effect on the removal performances. On the other hand, Cl − and NO 3 − had a beneficial effect on the WAO of the target pollutants. By combining quantum chemistry calculations and ESI-MS analysis, detailed degradation pathways of ID, BP, and BT could be proposed. It was concluded that ring breakage occurred on both the benzene and heterocyclic ring in the initial stage of WAO for all three substrates. [ABSTRACT FROM AUTHOR]

• Persulfate combined wet air oxidation (PWAO) is proposed to deep remove benzothiazole. • OH is firstly detected by electron paramagnetic resonance in wet air oxidation process. • OH plays a very important role in the PWAO process. • High COD removal is achieved with a large amount of microsphere polymers recycling. • The PWAO process has a lower operating cost than WAO in COD removal. Wet air oxidation (WAO) has an obvious advantage in treating wastewater with high concentration of organics, but harsh reaction conditions are required and the treatment efficiency has not reached a satisfactory level. Herein, we developed a low dosage of persulfate promoted WAO process (PWAO) to remove a model heterocyclic pollutant benzothiazole (BTH). The addition of persulfate remarkably enhanced the elimination of benzothiazole (BTH) and COD from water via degradation and polymerization. Under optimized operation condition (with 11.1 mM K 2 S 2 O 8 addition into WAO), about 65.0% of BTH converted into microsphere polymers and more than 94.6% COD was eliminated from water after polymers separation. Electron paramagnetic resonance (EPR) analysis and quenching experiments revealed that OH was effectively generated in a wide range of reaction temperature and it played the key role in BTH degradation and polymerization, while SO 4 − was detected at low temperature for its fast decomposition at high temperature. Quantum chemical calculation together with ultra-performance liquid chromatography with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS) analysis confirmed that the degradation and polymerization of BTH mainly started from the heterocyclic ring, followed by further oxidation or polymerization. Comparing with normal WAO process, the PWAO technology had an advantage in lower operating cost in removing per unit COD and carbon resource recycle, which indicates a promising prospect in treating wastewater with high concentration of heterocyclic compounds. [ABSTRACT FROM AUTHOR]

The nitrogen heterocyclic compounds (NHCs) are very toxic and widely used in many industries, while the treatment of NHCs in wastewater has not attracted enough concern till now. Here we studied the complete degradation of a typical NHCs, benzopyrazole (BP), in wet oxidation. The effects of different operation parameters, such as stirring speed, temperature, reaction time and initial pH, on BP degradation and chemical oxygen demand (COD) removal were studied. BP was totally degraded and the COD removal efficiency achieved 76.7%, after 120 min reaction at 220 °C with initial pH 6.5. Meanwhile, 81.7% of the nitrogen from BP was removed from the solution. The toxicity of the BP solution was reduced by 95.2% after wet oxidation at 240 °C for 180 min. The influences of coexisted NO 3 − , CO 3 2− , SO 4 2− and PO 4 3− ions were also investigated. With quantum chemical calculation and intermediates analysis by electrospray ionization mass spectrometry, a very detailed degradation pathway of BP in wet oxidation was proposed. [ABSTRACT FROM AUTHOR]

Heterogeneous photocatalysis and ozonation are robust advanced oxidation processes for eliminating organic contaminants in wastewater. The combination of these two methods is carried out in order to enhance the overall mineralization of refractory organics. An apparent synergism between heterogeneous photocatalysis and ozonation has been demonstrated in many literatures, which gives rise to an improvement of total organic carbon removal. The present overview dissects the heterogeneous catalysts and the influences of different operational parameters, followed by the discussion on the kinetics, mechanism, economic feasibility and future trends of this integrated technology. The enhanced oxidation rate mainly results from a large amount of hydroxyl radicals generated from a synergistically induced decomposition of dissolved ozone, besides superoxide ion radicals and the photo-induced holes. Six reaction pathways possibly exist for the generation of hydroxyl radicals in the reaction mechanism of heterogeneous photocatalytic ozonation. [ABSTRACT FROM AUTHOR]

The transformation of captopril (CAP), a widely-used thiol drug, was studied with the presence of dissolved model humic constituents (HCs) in a laccase-catalyzed system. Reaction products were analyzed by ultra-performance liquid chromatography coupled to time-of-flight mass spectrometry and condensed fukui function computation. CAP reacted with different model HCs in the enzymatic system for 1 h, ranging from 75% (syringic acid) to 96% ( p -coumaric acid). In the absence of HCs, only 15% of CAP was removed through self-coupling. The presence of HCs apparently changed the transformation of CAP in aqueous environment, and the HC reactive intermediates played an important role. First, during laccase catalysis, HCs with different structures were oxidized to produce reactive intermediates, including phenoxyl radical cation, ortho -, and para -quinone intermediates. Second, these intermediates were readily attacked by CAP via nucleophilic reactions, forming C–S–C covalent conjugates. More importantly, the standard reduction potential of these intermediates is a critical parameter, as PCA showed the highest reactivity to the nucleophilic addition reaction with CAP by forming phenoxy radical cations. While SYR showed the least reactivity due to the formation of para -quinone intermediates. Therefore, the functional groups on HCs could greatly influence the cross-coupling with CAP, as well as the type and stability of the coupling products. This work clearly demonstrated the transformation of CAP and other thiol drugs with the presence of HCs in aqueous environment, which is similar to the natural humification process. [ABSTRACT FROM AUTHOR]

Porous g-C 3 N 4 (PGCN) has attracted enormous attention due to its accessible nanoporous framework benefiting photocatalytic reactions. Here, we reported a one-pot template-free method to fabricate honeycomb-like PGCN by simply mixing ammonia chloride with the precursor of g-C 3 N 4 before calcination. The resulting PGCN exhibited obviously improved photocatalytic activity for p -hydroxybenzoic acid (PHBA) degradation under visible light due to its high surface area and enlarged band gap, but PHBA can hardly be mineralized in this process. Hence, for the first time, Vis/PGCN was coupled with ozone in this paper and the results showed that PGCN could trigger a vigorous synergy between photocatalysis and ozonation. Vis/O 3 /PGCN led to almost complete mineralization of PHBA with an ozone dosage of 1.5 mg/min, and the process could be further accelerated by increasing the ozone dosage. Such a remarkable mineralization enhancement was mainly attributed to the systematically promoted generation of non-selective hydroxyl radicals ( OH). The high CB level of PGCN benefited electron capture by ozone molecules, thus significantly enhanced charge separation and the decay of ozone into abundant OH. OH could vigorously react with PHBA and its ozone-recalcitrant intermediates such as the identified carboxylic acids, finally leading to thorough mineralization. Electrospray ionization–mass spectrometry was adopted to detect the evolution of degradation intermediates in ozonation and Vis/O 3 /PGCN, and the mineralization procedure from the original PHBA to CO 2 and H 2 O was comprehensively proposed. This study contributes to the integration of sunlight/PGCN with ozone as an efficient metal-free advanced oxidation process for water treatment. [ABSTRACT FROM AUTHOR]

Advanced oxidation processes (AOPs) are widely used as efficient technologies to treat highly toxic and harmful substances in wastewater. Taking the most representative aromatic compounds (monosubstituted benzenes, substituted phenols and heterocyclic compounds) as examples, this paper firstly introduces their structures and the structural descriptors studied in AOPs before, and the influence of structural differences in AOPs with different reactive oxygen species (ROS) on the degradation rate was discussed in detail. The structure-activity relationship of pollutants has been previously analyzed through quantitative structure-activity relationship (QSAR) model, in which ROS is a very important influencing factor. When electrophilic oxidative species attacks pollutants, aromatic compounds with electron donating groups are more favorable for degradation than aromatic compounds with electron donating groups. While nucleophilic oxidative species comes to the opposite conclusion. The choice of advanced oxidation processes, the synergistic effect of various active oxygen species and the used catalysts will also change the degradation mechanism. This makes the structure-dependent activity relationship uncertain, and different conclusions are obtained under the influence of various experimental factors. [Display omitted] • The structure of pollutants is a key factor affecting reactivity. • Typical structure descriptors and reactive oxidizing species are introduced. • The substrate-dependent reaction activity is affected by various factors. • Machine learning can be a new tool for this issue. [ABSTRACT FROM AUTHOR]

Highlights: [•] Electro-enzymatic method can effectively improve BPA removal with humic acid (HA). [•] Removal of BPA achieved 100% within 2min reaction at an optimal condition. [•] A novel mechanism of BPA removal is proposed during electro-enzymatic process. [•] HA provides a pathway of BPA self-polymers incorporated into HA matrix. [•] Chain reactions from BPA self-polymerization to cross-coupling oxidation. [Copyright &y& Elsevier]

Abstract: Controlling the morphology of transition-metal nanoparticles (TMNPs) can be an effective way to produce nanomaterials with favourable properties (activity and selectivity, etc.). Here we reported the shape control syntheses of TMNPs including Ru, Rh, Pd, Os, Ir, Pt, alloy PtRu, PtOs, and PtRuOs by co-reducing their metal precursors and Ag(I) ions in an organic medium. In this approach, Ag(I) ions were reduced first for their higher reduction potential, leading to the formation of spherical Ag nanoparticles. Then the subsequently reduced atoms of other transition-metals grew on the pre-existing Ag nanoparticles, resulting in the TMNPs with spherical or quasi-spherical shapes. In the absence of Ag precursors, the TMNPs obtained under same experimental conditions were dominated by irregular shapes, for example, rods, multi-pods, worm-like, or star-like, etc. The dependence of the property on the shape of the particles was also demonstrated using the catalytic oxidation of methanol as an example. [Copyright &y& Elsevier]