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Catalysts for the efficient catalytic decomposition of ozone to generate reactive free radicals to oxidize pollutants are needed. The graphite-supported CeO2 catalyst was optimally prepared, and its activity in ozonation was evaluated using the degradation of diethyl phthalate (DEP) as an index. The stability of CeO2/graphite catalyst and the influence of operating conditions on its catalytic activity were investigated, and the mechanism of CeO2/graphite catalytic ozonation was analyzed. CeO2/graphite had the highest catalytic activity at a Ce load of 3.5% and a pyrolysis temperature of 400 °C with the DEP degradation efficiency of 75.0% and the total organic carbon (TOC) removal efficiency of 48.3%. No dissolution of active components was found during the repeated use of CeO2/graphite catalyst. The ozone dosage, catalyst dosage, initial pH, and reaction temperature have positive effects on the DEP degradation by CeO2/graphite catalytic ozonation. The presence of tert-butanol significantly inhibits the degradation of DEP at an initial pH of 3.0, 5.8, or 9.0, and the experimental results of the •OH probe compound pCBA indicate that the CeO2/graphite catalyst can efficiently convert ozone into •OH in solution. The DEP degradation in the CeO2/graphite catalytic ozonation mainly depends on the •OH in the bulk solution formed by ozone decomposition. [ABSTRACT FROM AUTHOR]

Degradation of organics in high-salinity wastewater is beneficial to meeting the requirement of zero liquid discharge for coking wastewater treatment. Creating efficient and stable performance catalysts for high-salinity wastewater treatment is vital in catalytic ozonation process. Compared with ozonation alone, Mn and Ce co-doped γ -Al 2 O 3 could remarkably enhance activities of catalytic ozonation for chemical oxygen demand (COD) removal (38.9%) of brine derived from a two-stage reverse osmosis treatment. Experimental and theoretical calculation results indicate that introducing Mn could increase the active points of catalyst surface, and introducing Ce could optimize d -band electronic structures and promote the electron transport capacity, enhancing HO• bound to the catalyst surface ([HO•] ads) generation. [HO•] ads plays key roles for degrading the intermediates and transfer them into low molecular weight organics, and further decrease COD, molecular weights and number of organics in reverse osmosis concentrate. Under the same reaction conditions, the presence of Mn/ γ -Al 2 O 3 catalyst can reduce ΔO 3 /ΔCOD by at least 37.6% compared to ozonation alone. Furthermore, Mn-Ce/ γ -Al 2 O 3 catalytic ozonation can reduce the ΔO 3 /ΔCOD from 2.6 of Mn/ γ -Al 2 O 3 catalytic ozonation to 0.9 in the case of achieving similar COD removal. Catalytic ozonation has the potential to treat reverse osmosis concentrate derived from bio-treated coking wastewater reclamation. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Ozonation of oxalic acid in aqueous solution was conducted using multi-walled carbon nanotube (MWCNT) as the catalyst. The effects of operating conditions on the catalytic performance of MWCNT for oxalic acid removal were investigated. The catalyst dosage and the reaction temperature exert positive effects on the oxalic acid removal by MWCNT catalytic ozonation. The maximum degradation efficiency of oxalic acid is obtained with its initial concentration of 1.0mM. The degradation efficiency of oxalic acid increases with the initial pH value in the range of 1.0–3.0, whereas an opposite trend is observed when the initial pH value further increases from 3.0 to 6.1. The effect of initial pH value indicates that the oxalic acid adsorption on catalyst surface is essential for its effective removal by MWCNT catalytic ozonation. The inhibition of tert-butanol on the activity of MWCNT at initial pH 6.1 is more significant compared with the case of initial pH 3.0, suggesting that the contribution of bulk reactions to oxalic acid removal would be strengthened at a high initial pH value. [Copyright &y& Elsevier]

Abstract: The influences of treatment conditions, gas atmosphere (N2 and H2) and temperature (450°C and 950°C), on the surface properties and catalytic performance of carbon nanotube (CNT) were investigated for the degradation of oxalic acid in aqueous solution by the process of catalytic ozonation. No obvious change on the textural properties of CNT is found after heat treatment, while the results of Boehm titration clearly indicate the reduction of acidic groups and the increase of basic groups on CNT surface after heat treatment under different conditions, and then a significant improvement on oxalic acid removal by CNT catalytic ozonation is obtained. The heat treatment of CNT under H2 atmosphere is more effective in eliminating acidic groups and increasing basic groups than the case of N2 atmosphere at the same temperature, which results in higher catalytic activity and lower total organic carbon (TOC) release in ozonation correspondingly. A linear relationship is observed between the pH at the point of zero charge (pHPZC) of CNT and the rate constant for ozonation of oxalic acid in the presence of CNT with different treatments. It is suggested that heat treatment can increase the basic property of CNT, which can enhance the contribution of surface reactions to the whole reactions for ozonation of oxalic acid. [ABSTRACT FROM AUTHOR]

Abstract: Multi-walled carbon nanotube (MWCNT) has been used in the catalytic ozonation of oxalic acid in aqueous solution, which was pretreated using ozone and was characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption and Boehm titration. The effect of ozonation pretreatment on the catalytic activity of MWCNT and the ozonation mechanism of oxalic acid in the presence of MWCNT were investigated. The results indicate that with the increasing pretreatment time, the atom ratio of oxygen to carbon and the number of surface acid groups on MWCNT increase, while the catalytic activity of MWCNT on ozonation of oxalic acid decreases, suggesting that the chemical characteristics of MWCNT mainly determine its catalytic activity on oxalic acid mineralization. The inhibition of tert-butyl alcohol on the degradation of oxalic acid is slight for pristine MWCNT catalytic ozonation and this inhibition trend becomes more obvious when MWCNT was pretreated by ozone. A free radical mechanism was proposed which involves both surface reactions and bulk reactions between the oxalic acid and active species. [Copyright &y& Elsevier]

Abstract: Ozonation of oxalic acid in the presence of carbon nanotube (CNT) supported platinum (Pt/CNT) catalyst in aqueous solution was studied. The activity and stability of Pt/CNT, the influence of preparation conditions on Pt/CNT activity and the ozonation mechanism of oxalic acid with Pt/CNT were investigated. It was found that Pt/CNT was more active for oxalic acid removal and more resistant to ozonation compared with the case of activated carbon supported Pt catalyst. The Pt loading, reduction temperature and pyrolysis atmosphere significantly influenced the Pt/CNT activity, especially for pyrolysis atmosphere. By means of X-ray diffraction and X-ray photoelectron spectroscopy analysis, the aggregation of Pt and the existence of chemisorbed oxygen with Pt were found when the Pt/CNT catalyst was prepared by calcination, which are unfavorable for its performance. The CNT was oxidized and some acidic groups were generated in calcination, which also cause a decrease of Pt/CNT activity. A free radical mechanism was proposed which involves ozone decomposition and hydrogen peroxide formation for oxalic acid degradation on Pt/CNT. The redox couple of Ptred/Ptox was suggested to be crucial for the improvement of CNT activity. The Pt/CNT has a good stability after five re-uses without any leaching of Pt. [Copyright &y& Elsevier]

Abstract Combination of coagulation and ozonation was used to treat brine derived from a three-stage reverse osmosis (RO) process during coal gasification wastewater reclamation. Effects of operating parameters on the removals of total organic carbon (TOC), color and UV absorbance at 254 nm (A 254) were investigated during coagulation and ozonation. All the removal efficiencies of TOC, A 254 and color of FeCl 3 coagulant are about twice those of AlCl 3 coagulant at the same molar dose since almost all the molecular weight fractions of RO concentrate (ROC) could be removed effectively by FeCl 3 coagulant while only the fractions of molecular weight > 3 k Da could be removed effectively by AlCl 3 coagulant. The TOC removal increases with the increasing of ozone dose and reaction temperature during ozonation of ROC after coagulation pretreatment. TOC and color of ROC after pretreated by coagulation could be further removed effectively during ozonation since ozonation can significant reduce the fluorescence response of all the fractions of effluent organic matter in ROC. It is unexpectedly found that the increase of A 254 is observed after ozonation, this is because the intensity of absorbance at 254 nm by the low molecular weight transformation products (<2 k Da) increases significantly with the reaction time after 30 min. The coagulation coupling with ozonation is efficient in the removals of both TOC and color of ROC. Graphical abstract Image 1 Highlights • Coagulation coupling with ozonation is efficient in ROC treatment. • Removals of TOC, color and A 254 by FeCl 3 coagulant is about twice that of AlCl 3. • Ozonation is efficient in the removals of TOC and color of ROC after coagulation. • A 254 of the < 2 k Da transformation products increases significantly in ozonation. • Increasing ozone dose and reaction temperature are positive to remove TOC from ROC. [ABSTRACT FROM AUTHOR]

Diethyl phthalate (DEP) degradation by graphite supported metal oxide catalytic ozonation in aqueous solution was conducted. The activity and stability of graphite supported ZnO (ZnO/graphite) catalyst, the effects of preparation parameters and operational conditions on the activity of ZnO/graphite, and the mechanism of DEP degradation by ZnO/graphite catalytic ozonation were studied. ZnO/graphite has the highest activity on ozonation of DEP among the MnO x , FeO x , CrO x , CoO x , NiO x and ZnO supported on graphite catalysts, and it keeps excellent catalytic activity during reuse. ZnO/graphite catalyst prepared with 3.5% loading of zinc and calcined at 573 K in N 2 atmosphere has the highest activity, and the rodlike ZnO nanoparticles are formed on the graphite surface. The ZnO/graphite catalyst dose, the ozone dose and the initial solution pH exert positive effect on ozonation of DEP. The presence of ZnO/graphite enhances the utilization efficiency of ozone from 52.1% (ozonation alone) to 72.1%, and reduces more than half of the apparent activation energy for ozonation of DEP. It is proposed that the DEP oxidation occurs both in bulk solution and on the surface of ZnO/graphite catalyst, and OH plays a key role in bulk solution. [ABSTRACT FROM AUTHOR]

To fulfil the requirement of zero liquid discharge in the coal gasification wastewater treatment plant, evaporation and crystallization are usually adopted to treat reverse osmosis concentrate (ROC). However, their efficacies and the quality of their products are greatly affected by the organic matter concentration in coal gasification-ROC (CG-ROC). In the present study, ozonation with a commercial activated carbon (AC) as catalyst was conducted to further remove the organic matter in the concentrate originated from a three-stage RO after coagulation pretreatment. The kinetic model calculations were used for the first time to quantitatively evaluate the effect of matrix components on the performance of ozonation of CG-ROC at initial pH 9 and 11. The TOC removal difference among ozonation alone, ozonation alone followed by AC adsorption, and AC catalytic ozonation indicates that AC has a certain catalytic effect during ozonation of CG-ROC. The ΔO 3 /ΔTOC can be significantly reduced from 43.2 mg O 3 /mg TOC of ozonation alone to 16.2 mg O 3 /mg TOC of AC catalytic ozonation under the goal of achieving a similar TOC removal. The change of initial pH has little effect on the TOC removal during ozonation with AC, however, it has a remarkable effect on the TOC removal during ozonation alone. According to the results obtained in kinetic model calculations, high concentration of CO 3 •- would be generated from the reaction between HO• and CO 3 2− with a high concentration in solution, leads to the delay on the TOC removal in the early reaction stage during ozonation alone at initial pH 11. The results of A 254 and molecular weight (MW) distribution indicate that ozonation with AC is more efficient in removing the low MW intermediates absorption at 254 nm compared to that of ozonation alone. Ozonation with AC is more suitable for CG-ROC treatment since it is more energy saving, more efficient in organic matter removal, and more tolerated pH change and wastewater matrix compared to ozonation alone. Image 1 • Ozone-based technologies are potential for treating high Cl−-containing wastewater. • Energy consumption for ozonation of ROC can be clearly reduced by the AC addition. • The lag phenomenon during ozonation at pH 11 is due to the formation of many CO 3 •-. • Operational conditions have less effect on ozonation with AC than ozonation alone. [ABSTRACT FROM AUTHOR]