The Oxidation Mechanism of Aniline by Ozone Water and Ozone Micro-nano Bubble Water and Its Influencing Factors

Aniline is a kind of refractory contaminant that is difficult to be degraded by microorganisms. Ozone is a green and efficient reagent to oxidize aniline, while the ozone oxidation efficiency is restricted by the low ozone mass transfer rate. Micro-nano bubble ozonation has been developed as a new method to significantly improve the ozone utilization rate, while the characteristics of ozone micro-nano bubble when compared with dissolved ozone is not clear. The paper carried out batch experiments to research the oxidation effect of aniline by ozone water (OW) and ozone micro-nano bubble water (OMNBW), and found that the degradation rate of aniline by OMNBW was 2.8~5.9% higher than that by OW. The increase of pH had a negative effect on the degradation of aniline by OW and OMNBW. SO42-, Cl-, HCO­3- and Mg2+ could inhibit the degradation efficiency by 0.04%, 0.99%, 0.44% and 10.4% for OW, while the ratios were 1.1%, 6.4%, 4.1% and 1.5% for OMNBW. The addition of humic acid and fulvic acid could decrease the oxidation rate of aniline by 35% and 49% for OW, while the ratios were 41% and 62% for OMNBW. Through quenching experiment, it was found that the direct oxidation by ozone molecules and the indirect oxidation by superoxide radicals were main pathways for aniline oxidation by OW and OMNBW. This work provided a practical guide for the application of OMNBW in wastewater and groundwater treatment process.

Light alkane oxidation over well-defined active sites in metal–organic framework materials

We review structure–catalytic property relationships for MOF materials used in the direct oxidation of light alkanes, focusing specifically on the elucidation of active site structures and probes for reaction mechanisms.

Sorption of Arsenic(III) from wastewater using Prosopis spicigera L. wood (PsLw) carbon-polyaniline composite

Water contamination by toxic heavy metal ions causes a serious public health problem for humans. The present work reports the development of a new adsorbent of PsLw carbon-polyaniline composite by direct oxidation polymerisation of aniline with PsLw carbon for the removal of arsenic (As). The structure and morphologies of the adsorbent were characterised by Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The ability of the adsorbent for the removal of As(III) was estimated by batch and kinetic studies. The optimum adsorption behaviour of the adsorbent was measured at pH=6.0. The equilibrium process was found to be in good agreement with Langmuir adsorption isotherm and the maximum adsorption capacity was 98.8 mg/g for an initial concentration of 60 mg/L at 30 °C. The kinetic study followed pseudo-second-order kinetics. Thermodynamic parameters predict the spontaneous, feasible and exothermic nature of adsorption. Column operation was carried out to remove As(III) bulk and column data obeys the Thomas model. The results indicated that PsLw carbon-polyaniline composite can be employed as an efficient adsorbent than polyaniline for removal of As(III) from wastewater.

The Regulation of O2 Spin State and Direct Oxidation of CO at Room Temperature Using Triboelectric Plasma by Harvesting Mechanical Energy

Oxidation reactions play a critical role in processes involving energy utilization, chemical conversion, and pollutant elimination. However, due to its spin-forbidden nature, the reaction of molecular dioxygen (O2) with a substrate is difficult under mild conditions. Herein, we describe a system that activates O2 via the direct modulation of its spin state by mechanical energy-induced triboelectric corona plasma, enabling the CO oxidation reaction under normal temperature and pressure. Under optimized reaction conditions, the activity was 7.2 μmol h−1, and the energy consumption per mole CO was 4.2 MJ. The results of kinetic isotope effect, colorimetry, and density functional theory calculation studies demonstrated that electrons generated in the triboelectric plasma were directly injected into the antibonding orbital of O2 to form highly reactive negative ions O2−, which effectively promoted the rate-limiting step of O2 dissociation. The barrier of the reaction of O2− ions and CO molecular was 3.4 eV lower than that of O2 and CO molecular. This work provides an effective strategy for using renewable and green mechanical energy to realize spin-forbidden reactions of small molecules.

Concentration Polarization Quantification and Minimization in Cork Process Wastewater Ultrafiltration by an Ozone Pretreatment

Concentration polarization and membrane fouling have been identified as the main problems during the ultrafiltration treatment of cork processing wastewaters. These problems drastically reduce the permeate fluxes and, therefore, their potential applications. In this work, a soft ozonation pretreatment was applied to minimize these undesirable effects. A new systematic study was carried out for membranes with different molecular weight cut-offs and at different operating conditions to monitor and quantify the concentration polarization caused by the wastewater’s remaining ozonated compounds. Film theory was used to correlate the mass transfer coefficient, k, and the intrinsic rejection coefficient, f′, with the resistance introduced by concentration polarization. The ultrafiltration treatment was carried out under varying hydrodynamic operating conditions (circulating flow rates of 100–200 L/h) and transmembrane pressures (1–3 bar) for a set of four cellulose acetate membranes covering a wide range of molecular weight cut-offs (5000–100,000 Da) and hydraulic permeabilities (25–110 kg/h/m2/bar). The ozone pretreatment (at wastewater pH) reduced the phenolic content selectively (direct oxidation) by more than 50%, reducing membrane fouling and concentration polarization and increasing permeate fluxes (by 22–45%) and mass transfer coefficients (up to six times).

Electrocatalytic Degradation of Sulfameth Thiadiazole by GAC@Ni/Fe Three-Dimensional Particle Electrode

In this work, GAC@Ni/Fe particle electrodes were prepared and employed for the degradation of Sulfamethylthiadiazole (SMT) by three-dimensional electrocatalytic technology.The effects of particle electrode bi-metal loading ratio, cell voltage, particle electrode dosage, electrode plate spacing and SMT initial concentration on SMT removal were studied.In addition, GAC@Ni/Fe particle electrode was analyzed by the scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), X-ray photoelectron spectrometer (XPS) and Fourier transform infrared spectrometer (FTIR) to characterize . which indicated that a significant amount of Iron-nickel oxide were formed on the surface of GAC@Ni/Fe particle electrode.The results indicated that when the nickel-iron loading ratio is 1:1, the SMT removal effect is the best, and the removal rate can reach 90.89% within 30 minutes,Compared with the granular activated carbon without bimetal, the removal efficiency is increased by 37.58%. The degradation of SMT in the GAC@Ni/Fe particle three-dimensional electrode reactor is the joint result of both direct oxidation and indirect oxidation. The contribution rates of direct oxidation of anode and particle electrode and indirect oxidation of ·OH in the degradation are 32%, 27% and 41%, respectively. Based on the intermediate detected by ultra high liquid chromatography and the calculation of bond energy of SMT molecule by Gauss software，the degradation pathway of SMT in the GAC@Ni/Fe three-dimensional electrode reactor is proposed. This research provides a green, healthy and effective method for removing sulfonamide micro-polluted wastewater.

Synthesis of Ce/MgO Catalysts for Direct Oxidation of Hibiscus cannabinus Stalks to Vanillin

One possible method of producing vanillin from biomass is through controlled oxidation of lignin. Direct oxidation of kenaf stalks was chosen without having to separate the cellulose and hemicellulose components from the lignocellulosic biomass. This makes the process greener, as well as saving time. In this paper, Ce/MgO catalysts were developed for oxidation of kenaf stalks and kenaf lignin under microwave irradiation. The catalysts were characterized for their physicochemical properties using XRD and N2 adsorption–desorption isotherms. The synthesized MgO showed the presence of diffraction peaks assigned to cubic MgO while the 30Ce/MgO catalysts showed the presence of cubic fluorite of CeO2. N2 adsorption–desorption isotherms showed that all catalysts possess Type III isotherm according to IUPAC classification, indicating a nonporous structure. All catalysts were tested for direct oxidation of kenaf stalks under 300 W of microwave irradiation using H2O2 as the oxidizing agent at pH 11.5 and temperatures between 160 and 180 °C for 10–30 min with 5–15% catalyst loading. The highest vanillin yields of 3.70% and 2.90% for extracted lignin and direct biomass oxidation were achieved using 30Ce/MgO-48. In comparison, 7.80% and 4.45% were obtained using 2N of NaOH homogeneous catalyst for extracted lignin and direct biomass, respectively, at 170 °C for 20 min. The reusability test shows that 30Ce/MgO can be used up to three cycles without significant loss in catalytic activity. Other compounds detected were 4-vinylguaiacol, syringol and syringaldehyde.

Synergistic Effect of Neighboring Fe and Cu Cation Sites Boosts FenCum-BEA Activity for the Continuous Direct Oxidation of Methane to Methanol

Direct oxidation of methane to methanol (DMTM), constituting a major challenge for C1 chemistry, has aroused significant interest. The present work reports the synergistic effect of neighboring [Fe]--[Cu] cations, which can significantly boost the CH3OH productivity (100.9 and 41.9 → 259.1 μmol∙g−1cat∙h−1) and selectivity (0.28 and 17.6% → 71.7%) of the best performing Fe0.6%Cu0.68%-BEA (relative to monomeric Fe1.28%- and Cu1.28%-BEA) during the continuous H2O-mediated N2O DMTM. The combined experimental (in situ FTIR, D2O isotopic tracer technique) and theoretical (DFT, ab initio molecular dynamics (AIMD)) studies reveal deeper mechanistic insights that the synergistic effect of [Fe]--[Cu] can not only significantly favor active O production (ΔG = 0.18 eV), but also efficiently motivate the reaction following a H2O proton-transfer route (ΔG = 0.07 eV), eventually strikingly promoting CH3OH productivity/selectivity. Generally, the proposed strategy by employing the synergistic effect of bimetallic cations to modify DMTM activity would substantially favor other highly efficient catalyst designs.