Huangzhao Wei

Prussian blue/TiO2 nanocomposites as a heterogeneous photo-Fenton catalyst for degradation of organic pollutants in water

Nowadays, a lot of research focuses on accelerating FeII/FeIII redox cycles to increase the pseudo first-order rates of the Fenton reaction. Here, Prussian blue/titanium dioxide nanocomposites (PB/TiO2 NPs) were designed as heterogeneous photo-Fenton catalysts to increase the FeII recovery in degrading organic contaminants in water for the first time. The PB/TiO2 NPs were characterized by various analytical techniques to obtain the optimum ratio of PB and TiO2 for efficient degradation of organics. The performance of the catalysts was tested by following the removal of rhodamine B dye, salicylic acid, m-cresol, and isophorone under various conditions (pH, ratios of PB and TiO2, H2O2, and temperature). Formation of the intermediates of iron (FeII/FeIII) in the studied system using Mossbauer spectroscopy was explored for the first time and presents important insights into the relevant catalytic phenomena. The generation of ˙OH radicals in the reaction system was identified using electron paramagnetic resonance spectroscopic techniques. Results demonstrated that the developed PB/TiO2 NPs were stable and could degrade organic contaminants in water efficiently.

The degradation of Isophorone by catalytic wet air oxidation on Ru/TiZrO4

The catalyst Ru/TiZrO(4) was applied in the degradation of Isophorone by catalytic wet air oxidation. Mathematical models for the effects of reaction conditions on the Isophorone degradation by catalytic wet air oxidation were developed using a response surface methodology. A model was obtained for each response with multiple regression analysis and then was refined. Analysis of variance revealed that the models developed were adequate. The validity of the models was also verified by experimental data. Analysis of response surface showed that total organic carbon removal and Isophorone conversion were significantly affected (P≤0.01) by reaction time, temperature and their interactions, and affected (P≤0.05) by the square of reaction time. The point of zero charge of Ru/TiZrO(4) catalyst was about 1.72. The total organic carbon removal and Isophorone conversion had a great association with the zeta potential of Ru/TiZrO(4) catalyst. Finally, the degradation pathway of Isophorone in catalytic wet air oxidation was proposed. Within 410 h, the total organic carbon removal remained above 95%, indicating that the Ru/TiZrO(4) catalyst had a good stability.

Catalytic wet air oxidation of m-cresol over a surface-modified sewage sludge-derived carbonaceous catalyst

Sewage sludge-derived carbonaceous materials (SW) treated with different kinds of acids were used as catalysts for catalytic wet air oxidation (CWAO) of m-cresol. The SW catalysts were characterized by XRF, XRD, FTIR, XPS and TPD-MS. The results showed that SW treated with HNO3 (HNO3-SW) exhibited the best catalytic activity. When the initial concentration of m-cresol was 5000 mg L−1, the conversion of m-cresol reached 99.0% with HNO3-SW after 90 min at 160 °C and 0.66 MPa oxygen. Continuous experiments were carried out for 8 d to investigate the durability and catalytic performance of HNO3-SW in CWAO reaction. Some correlation was observed between the conversion of m-cresol and the content of carboxyl groups, indicating that the carboxyl group might play a key role in determining the catalytic activity of SW catalysts in CWAO reaction. Based on the intermediate products identified by GC-MS, HPLC-MS, IC and HRMS analyses, the oxidation pathways of m-cresol in CWAO were proposed.

Surface modification of sewage sludge derived carbonaceous catalyst for m-cresol catalytic wet peroxide oxidation and degradation mechanism

Sewage sludge derived carbonaceous materials (SWs) treated with different kinds of acid were used as the catalysts for catalytic wet peroxide oxidation (CWPO) of m-cresol in batch reactor and continuous reactor, respectively. The results showed that SW treated with nitric acid (HNO3-SW) and sulfuric acid (H2SO4-SW) exhibited high catalytic activity in a CWPO reaction. The conversion of m-cresol reached 100%, after CWPO reaction for 3 h at an initial pH of 7 and a temperature of 25 °C over a H2SO4-SW catalyst. The elements content and chemical state of SWs treated with different kinds of acids were measured by XRF, XPS and Mossbauer spectra, the results implied that ferric iron and surface functional groups might play the main role in m-cresol degradation. The intermediate oxidation products were identified by in situ NMR, GC-MS, IC and HRMS analyses. Based on a free-radical reaction mechanism, a m-cresol oxidation pathway in CWPO was proposed.

Effect of TiO2 on Ru/ZrO2 catalysts in the catalytic wet air oxidation of isothiazolone

For the first time, Ru/xTiZrO4 catalysts were evaluated in the catalytic wet air oxidation (CWAO) reaction of isothiazolone. The structures of the Ru/xTiZrO4 catalysts were examined using Brunauer–Emmett–Teller (BET) measurements, X-ray diffraction, temperature programmed reduction, CO chemisorption, mechanical strength analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, zeta-potential measurement and thermogravimetric analysis. The effect of TiO2 content on the activity for TOC removal and mechanical and chemical stability of the Ru/xTiZrO4 catalysts was evaluated. The results indicated that the addition of TiO2 as a second oxide component hindered the crystallization of pure ZrO2, improved the crushing strength of the catalyst and increased the bonding strength of RuOx and the support. For Ru/xTiZrO4 catalysts (x 0.2, the addition of TiO2 reduced the activity for TOC removal; however, the mechanical stability of the catalysts was enhanced. The Ru/0.2TiZrO4 catalyst exhibited high activity for TOC removal and good mechanical stability and was therefore selected as the optimal catalyst to treat isothiazolone wastewater using CWAO. For the reaction temperature of 200 °C and LHSV of 2 h−1, the isothiazolone conversion, TOC and TN removal reached 100%, 82.6% and 44.5%, respectively. Finally, the degradation pathway of isothiazolone in CWAO was proposed. Throughout the 240 h evaluation period, the isothiazolone conversion and total organic carbon removal remained at values greater than 99% and 82%, respectively, indicating that the Ru/0.2TiZrO4 catalyst exhibited good chemical stability.

The optimization, kinetics and mechanism of m-cresol degradation via catalytic wet peroxide oxidation with sludge-derived carbon catalyst

The sludge-derived carbon catalyst modified with 0°C HNO3 solution was tested in catalytic wet peroxide oxidation of m-cresol (100mgL-1) with systematical mathematical models and theoretical calculation for the first time. The reaction conditions were optimized by response surface methodology (RSM) as T=60°C, initial pH=3.0, C0,H2O2(30%)=1.20gL-1 (lower than the stoichiometric amount of 1.80gL-1) and Ccat=0.80gL-1, with 96% of m-cresol and 47% of TOC converted after 16min and 120min of reaction, respectively, and ξ (mg TOC/g H2O2 fed)=83.6mg/g. The end time of the first kinetic period in m-cresol model was disclosed to be correlated with the fixed residue m-cresol concentration of about 33%. Furthermore, the kinetic constants in models of TOC and H2O2 exactly provide convincing proof of three-dimensional response surfaces analysis by RSM, which showed the influence of the interaction between organics and H2O2 on effective H2O2 utilization. The reaction intermediates over time were identified by gas chromatography-mass spectrometer based on kinetics analysis. Four degradation pathways for m-cresol were proposed, of which the possibility and feasibility were well proven by frontier molecule orbital theory and atomic charge distribution via density functional theory method.

Influence of support on the catalytic properties of Pt–Sn–K/θ-Al2O3 for propane dehydrogenation

A study on the performance of Pt(0.3 wt%) Sn(0.2 wt%) K(0.5 wt%) catalysts supported on four different theta-Al2O3 for propane dehydrogenation is reported in this study. The theta-Al2O3 used as supports were prepared by four different methods as (a) calcination of the commercial gamma-Al2O3 at 1223 K for 12 h, (b) synthesis by hydrochloric acid reflux method, (c) precipitation of Al(NO3)(3)center dot 9H(2)O with ammonia solution and (d) extrusion use pseudo-boehmite powder, respectively. They were characterized by using XRD, BET, SEM, H-2-TPR, NH3-TPD, CO-chemisorption, XPS and TG-DTA methods to study which characteristics of the carrier will affect the performance of the catalyst. The results show that high acidity and strong interactions of the Sn support can improve the propane dehydrogenation activity of the catalyst, large pore volume and large pore diameter can enhance the stability of the catalyst. Al2O3 synthesized by method (b) has the largest pore volume, pore diameter, relatively high surface acidity and strong interaction with Sn, which meant the catalyst with the support prepared by method (b) showed the highest propane conversion and superior selectivity. The average conversion is 38.6% and the average selectivity is 95.2% during the reaction time of 25 h.

Low temperature modified sludge-derived carbon catalysts for efficient catalytic wet peroxide oxidation of m-cresol

A method for recycling sewage sludge was investigated to prepare catalysts with a desired shape for use in the catalytic wet peroxide oxidation (CWPO) reaction. Sludge-derived carbon (SC) was first modified with HNO3 solutions under different conditions; only the SCs modified at or below 0 °C retained their columnar shape instead of corroding into a powder. The prepared samples were tested in the CWPO reaction using m-cresol as the target pollutant. The highest degradation rate of 97.6% after 30 min was found for the sample modified at 0 °C with 6 mol L−1 HNO3 for 24 h (SC-T0) with the stoichiometric dose of hydrogen peroxide required for the complete mineralization of m-cresol. The sample modified at the commonly used temperature of 60 °C converted only 17.7% of the m-cresol after reaction. The physical and chemical properties of the SCs were fully characterized. All the modified samples benefited from the pore expansion effect of HNO3 and had a larger specific surface area than the original SC. For SC samples with abundant surface oxygen groups and iron species, treatment with HNO3 at 0 °C allowed the sample to retain abundant basic surface oxygen groups and iron species in addition to removing large amounts of negatively charged species, thus achieving the effective utilization of H2O2 and improving the catalytic activity. The oxidation route for m-cresol in the presence of SC-T0 was also studied with the assistance of density functional theory. The ability to regenerate SC-T0 without any loss of performance was demonstrated over three runs.

Sewage-sludge-derived carbonaceous materials for catalytic wet hydrogen peroxide oxidation of m-cresol in batch and continuous reactors.

In this study, four sewage-sludge-derived carbonaceous materials (SWs) were evaluated for their catalytic wet hydrogen peroxide oxidation (CWPO) performance of m-cresol in batch reactor and continuous reactor, respectively. The SWs were produced by carbonization (SW); carbonization with the addition of CaO (CaO-SW); HNO3 pretreatment (HNO3-SW) and steam activation (Activated-SW). The properties of SW catalysts were assessed by thermogravimetric analysis, Brunauer–Emmett–Teller, Fourier Transform Infrared Spectroscopy, X-ray Fluorescence, Scanning electron microscopy, energy dispersive X-ray analysis and zeta potential. The results showed that SW treated by HNO3 (HNO3-SW) had a high conversion of m-cresol in batch reactor and continuous reactor, respectively. Under the conditions of batch reaction (Cm-cresol = 100 mg L−1, CH2O2 = 15.7 mmol L−1, initial pH=7.0, 0.5 g L−1 catalyst, 80°C, 180 min adsorption and 210 min oxidation), the conversion of m-cresol reached 100% and total organic carbon removal was 67.1%. It had a high catalytic activity and stability on the treatment of m-cresol in CWPO for more than 1100 h. Furthermore, a possible reaction mechanism for the oxidation of m-cresol to 2-methyl-p-benzoquinone by CWPO was proposed.

Extended study of ammonia conversion to N2 using a Ru/0.2TiZrO4 catalyst via catalytic wet air oxidation

As one of the key components of waste disposal in conventional water treatment processes, (NH4)2SO4 (NH3–N concentration = 4390 mg L−1, pH = 5.3) was selected as a model compound. The effectiveness of various heterogeneous catalysts was evaluated by catalytic wet air oxidation (CWAO) in batch reactors. Then, the activity of NH3–N decomposition was compared systematically in regard the loading amount of noble metal, reaction conditions and concentration of substrate in the continuous reactors. The results showed that under acidic conditions, the elimination of refractory aqueous ammonia can be significantly enhanced upon the addition of a Ru/0.2TiZrO4 catalyst. After 150 min of reaction, NH3–N was totally decomposed to N2 as the final product and no undesirable nitrites or nitrates were detected. The effluent was strongly acidic and H2SO4 produced in the effluent could adsorb exhausted NH3 again to realize green cyclic economy. When combined with density functional theory (DFT), the mechanism of (NH4)2SO4 degradation was assumed showing that NH4+ instead of aqueous ammonia was the necessary active nitrogen-species participating in the CWAO reaction and both the NO2− and NO3− generated during the oxidation process can react with NH4+ in the solution and produce N2. The charts of the related electron cloud were displayed to confirm the possibility and feasibility of the abovementioned reactions according to frontier molecule orbital theory. It can be concluded that CWAO is superior because N2 was formed as the only final product in our study and can be considered as a potential method to remove large amounts of NH3–N in wastewater.