Fig 5 - available via license: Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
Content may be subject to copyright.
The FTIR spectra of 50 mg/L benzoic acid at various sonication times. The peaks at 1732 cm 1 and 1694 cm 1 are the carboxylic acid peaks.
Source publication
Propelled by enormous increase in demand for fuel sources, Canadian oil sands are becoming increasingly important as a fuel source due to their abundance and upgrading capability. However, extraction of bitumen, a high acid crude (HAC) oil, requires 2-3 units of water per unit of oil resulting in naphthenic acid (NA)-rich oil sands process affected...
Context in source publication
Context 1
... Ortho-addition experiences steric hindrance, H-bond formation and the electron withdrawing effects of the carboxyl group (also seen in paraaddition) making the meta additions the most likely site for OH • electrophilic attack [48,29,[49][50][51][52]. The FTIR spectra provides detailed insight into which path the degradation is likely to take. Fig. 5 shows the carboxylic acid peaks for 50 mg/L which decrease with time from 0 to 30 min, increase at 60 min and flatten altogether at 240 min. The aromatic stretching section clarifies that the right side pathway in Fig. 4 is predominant. For 0 and 15 min, the carboxylic acid peaks at 1732 cm 1 and 1694 cm 1 are strong along with the ...
Citations
... More complex cyclic hydrocarbons undergo hydroxylation and degradation. The mechanism is critical for unit operation design [3]. Shende et al. targeted perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). ...
... This study explores the QM screening strategy through the known degradation pathway of benzoic acid and its intermediates via a theoretical approach using DFT studies to complete mineralization from previous works and our previous study [5]. Geometry optimizations, frequency calculations, transitions states, interaction energies, Mulliken charges, Hirshfeld population analysis, dipole moments, and polarizabilities have all been calculated by DFT method. ...
... A reaction shift towards OH • radicals may be enhanced by the introduction of ozone or similar oxidants into the process. It was reported and confirmed [5] that during sonication, model organic acids such as benzoic acid, due to their volatile and hydrophobic nature, diffuse to the cavitation bubble and decompose by pyrolysis and/or OH • degradation by a range of steps as shown in Fig. 1. ...
... Ten NEB images were used to create a detailed reaction profile. Based on the empirical identification of degradation compounds from Part I [5], a suggested transition state was applied in ring-opening reaction steps to facilitate the reaction progress within NEB-TS and avoid radical attacks expected due to the limitations of the NEB-TS approach. Avogadro auto optimization was used to obtain the suggested transition states of the targeted reaction by selecting an arbitrary step immediately following radical attack. ...
In Part I, we outlined the importance of sustainable sonochemical treatment to intensify oil sands process affected water (OSPW) treatment empirically and hypothesized degradation pathways. Herein, we elucidate the formation of intermediate products with well-defined molecular level solutions. Proposed mechanisms describe hydroxylation, decarboxylation and bond scission which drive the degradation of intermediates towards mineralization. This comprehensive first study on in silico screening of sonochemical degradation investigates quantum methods using density functional theory to explain the postulated degradation mechanisms through a theoretical radical attack approach, based on condensed Fukui reactivity indicators. A nudged elasticity band (NEB) approach is applied to find a minimum energy path (MEP), allowing the determination of intermediate products and energy barriers associated with naphthenic acid degradation. This approach provides structures and energies of the breakdown compounds formed along the reaction pathway enabling the determination of molecular reaction kinetics.
In continuation of Part 1, the focus of this study is to evaluate sonochemically-induced hydroxyl radical (OH•) reactions of benzoic acid using density functional theory. Hydroxylation and decarboxylation mechanisms of the model naphthenic acid compound and its intermediates were simulated to determine the prospective pathway to ideal mineralization. DFT was applied to calculate interaction energies, Mulliken charges, Hirshfeld population analysis, dipole moments, frontier orbitals, and polarizability. Electronic properties and frontier orbital trends were also compared to computational work by Riahi et al. [1] to confirm the transition states by Nudged Elastic Band Transition State theory (NEB-TS). In combination with Hirshfeld Population analysis, Fukui indices suggest a more linear degradation pathway narrowed down from earlier experimental work by Singla et al. [2]. The linear free energy relationship for the newly suggested computational benzoic acid degradation can be determined by lnkTST/W=-1.677ΔG-15.41 with a R² of 0.9997 according to classic transition state theory and Wigner tunneling. This computational method can be used to explore possible degradation pathways of other NAs and bridges molecular-to-macroscale sonochemical degradation of NA’s through a manifestation of molecular solutions.
This study aims to investigate the sonocatalytic activation of hydrogen peroxide (H2O2) using Cr2AlC MAX phase prepared by the reactive sintering process. The hexagonal structure of the crystalline MAX phase was confirmed by X-ray diffraction. Moreover, the compacted layered structure of the MAX phase was observed via scanning electron microscopy and high-resolution transmission electron microscopy. Under the desired operating conditions, Cr2AlC MAX phase (0.75 g/L) showed suitable potential to activate H2O2 (1 mmol/L) under sonication, thereby allowing a considerable removal efficiency for various organic pollutants, including dimethyl phthalate (69.1%), rifampin (94.5%), hydroxychloroquine (100%), and acid blue 7 (91.5%) with initial concentration of 15 mg/L within 120 min of treatment. Kinetic analysis proved that the degradation reaction followed pseudo-first-order kinetics. Scavenging tests demonstrated that hydroxyl radicals and singlet oxygen were effective species during degradation. Furthermore, a probable mechanism for dimethyl phthalate degradation was suggested according to gas chromatography-mass spectroscopy and nuclear magnetic resonance analyses. The obtained results confirmed the capability of the triple Cr2AlC/H2O2/US process as a promising method for treating contaminated water.
