Xiaoliang Liang

The decolorization of Acid Orange II in non-homogeneous Fenton reaction catalyzed by natural vanadium-titanium magnetite

The catalytic activity of natural vanadium-titanium magnetite was investigated in the decolorization of Acid Orange II by non-homogeneous Fenton process. The natural catalysts purified by magnetic separation were characterized using X-ray diffraction (XRD), polarizing microscope, X-ray absorption fine structure (XAFS) analysis and Mössbauer spectroscopy. The obtained results show that the natural samples after magnetic separation mainly contain titanomagnetite, with a small amount of ilmenite and chlorite. Titanomagnetite is doped with vanadium, whose the valency is mainly +3 and occupies the octahedral site. Batch decolorization studies were performed to evaluate the influences of various experimental parameters like initial pH, the amount of catalyst and initial concentration of hydrogen peroxide on the decolorization efficiency of Acid Orange II. The decolorization of the dye mainly relied on degradation. The degradation efficiency was strongly dependent on pH of the medium where it increased as the pH decreased in acid range. The increase of catalyst and hydrogen peroxide could accelerate the degradation. The catalytic property of natural vanadium-titanium magnetite in the degradation of Acid Orange II was stronger than that of synthetic magnetite (Fe(3)O(4)). The catalytic activity of the natural samples was greatly related to the titanomagnetite content. The degradation process was dominated by heterogeneous Fenton reaction, complying with pseudo-first-order rate law. The natural catalyst has a good catalytic stability.

Heterogeneous UV/Fenton degradation of TBBPA catalyzed by titanomagnetite: Catalyst characterization, performance and degradation products

Tetrabromobisphenol A (TBBPA), a widely used brominated flame retardant, could negatively affect various aspects of mammalian and human physiology, which triggers effective techniques for its removal. In this work, the degradation characteristics of TBBPA in heterogeneous UV/Fenton reaction catalyzed by titanomagnetite (Fe(3-x)Ti(x)O₄) were studied. Batch tests were conducted to evaluate the effects of titanomagnetite dosage, H₂O₂ concentration and titanium content in magnetite on TBBPA degradation. In the system with 0.125 g L⁻¹ of Fe₂.₀₂Ti₀.₉₈O₄ and 10 mmol L⁻¹) of H₂O₂, almost complete degradation of TBBPA (20 mg L⁻¹) was accomplished within 240 min UV irradiation at pH 6.5. The titanium incorporation obviously enhanced the catalytic activity of magnetite. As shown by the XRD and XANES results, titanomagnetite had a spinel structure with Ti⁴⁺ occupying the octahedral sites. On the basis of the degradation products identified by GC-MS, the degradation pathways of TBBPA were proposed. TBBPA possibly underwent the sequential debromination to form TriBBPA, DiBBPA, MonoBBPA and BPA, and β-scission to generate seven brominated compounds. All of these products were finally completely removed from reaction solution. In addition, the reused catalyst Fe₂.₀₂Ti₀.₉₈O₄ still retained the catalytic activity after three cycles, indicating that titanomagnetite had good stability and reusability. These results demonstrated that heterogeneous UV/Fenton reaction catalyzed by titanomagnetite is a promising advanced oxidation technology for the treatment of wastewater containing TBBPA.

The contribution of vanadium and titanium on improving methylene blue decolorization through heterogeneous UV-Fenton reaction catalyzed by their co-doped magnetite

This study investigated the methylene blue (MB) decolorization through heterogeneous UV-Fenton reaction catalyzed by V-Ti co-doped magnetites, with emphasis on comparing the contribution of V and Ti cations on improving the adsorption and catalytic activity of magnetite. In the well crystallized spinel structure, both Ti(4+) and V(3+) occupied the octahedral sites. Ti(4+) showed a more obvious effect on increasing specific surface area and superficial hydroxyl amount than V(3+) did, resulting in a significant improvement of the adsorption ability of magnetite to MB. The UV introduction greatly accelerated MB degradation. And magnetite with more Ti and less V displayed better catalytic activity in MB degradation through heterogeneous UV-Fenton reaction. The transformation of degradation products and individual contribution from vanadium and titanium on improving adsorption and catalytic activity of magnetite were also investigated. These new insights are of high importance for well understanding the interface interaction between contaminants and metal doped magnetites, and the environmental application of natural and synthetic magnetites.

Occurrence, fate and ecological risk of chlorinated paraffins in Asia: A review

Chlorinated paraffins (CPs), complex mixtures of polychlorinated alkanes, are widely used in various industries and are thus ubiquitous in the receiving environment. The present study comprehensively reviewed the occurrence, fate and ecological risk of CPs in various environmental matrices in Asia. Releases from the production and consumption of CPs or CP-containing materials, wastewater discharge and irrigation, sewage sludge application, long-range atmospheric transport and aerial deposition have been found to be most likely sources and transport mechanisms for the dispersion of CPs in various environmental matrices, such as air, water, sediment, soil and biota. CPs can be bioaccumulated in biota and biomagnified through food webs, likely causing toxic ecological effects in organisms and posing health risks to humans. Inhalation, dust ingestion and dietary intake are strongly suggested as the major routes of human exposure. Research gaps are discussed to highlight the perspectives of future research to improve future efforts regarding the analysis of CPs, the environmental occurrence and elimination of CPs, the total environmental pressure, and the risks to organisms and populations.

The distinct effects of Mn substitution on the reactivity of magnetite in heterogeneous Fenton reaction and Pb(II) adsorption

In this study, a series of Mn substituted magnetites were synthesized and used in catalyzing the heterogeneous Fenton degradation of acid orange II and Pb(II) adsorption, in order to investigate the effect of Mn substitution on the reactivity of magnetite. The valence and local environment of both Fe and Mn in the spinel structure of magnetite were investigated by X-ray absorption fine structure (XAFS) spectroscopy. The incorporation of Mn did not change the valence and local structure of Fe in the synthetic magnetite, while Mn was in the valences of +2 and +3. The Mn distribution on the octahedral sites of magnetite surface increased with the increase in Mn content. The Mn introduction led to an improvement of catalytic activity of magnetite. The sample with the minimum Mn content displayed the best efficiency in OH production and the degradation of acid orange II, while the other substituted samples did not show obvious difference in their catalytic performance. The adsorption capacity of magnetite samples toward Pb(II) gradually increased with the increase in Mn content. The above influences of Mn substitution on the reactivity of magnetite were discussed in views of the variations in microstructural environment and physicochemical properties.

Simultaneous adsorption of Cd(II) and phosphate on Al13 pillared montmorillonite

Al13 pillared montmorillonites (AlPMts) prepared with different Al/clay ratios were used to remove Cd(II) and phosphate from aqueous solution. The structure of AlPMts was characterized by X-ray diffraction (XRD), Thermogravimetric analysis (TG), and N2 adsorption–desorption. The basal spacing, intercalated amount of Al13 cations, and specific surface area of AlPMts increased with the increase of the Al/clay ratio. In the single adsorption system, with the increase of the Al/clay ratio, the adsorption of phosphate on AlPMts increased but that of Cd(II) decreased. Significantly enhanced adsorptions of Cd(II) and phosphate on AlPMts were observed in a simultaneous system. For both contaminants, the adsorption of one contaminant would increase with the increase of the initial concentration of the other one and increase in the Al/clay ratio. The enhancement of the adsorption of Cd(II) was much higher than that of phosphate on AlPMt. This suggests that the intercalated Al13 cations are the primary co-adsorption sites for phosphate and Cd(II). X-ray photoelectron spectroscopy (XPS) indicated comparable binding energy of P2p but a different binding energy of Cd3d in single and simultaneous systems. The adsorption and XPS results suggested that the formation of P-bridge ternary surface complexes was the possible adsorption mechanism for promoted uptake of Cd(II) and phosphate on AlPMt.

The variation of cationic microstructure in Mn-doped spinel ferrite during calcination and its effect on formaldehyde catalytic oxidation

In this study, a series of Mn substituted spinel ferrites calcinated at different temperatures were used as catalysts for the oxidation of formaldehyde (HCHO). X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and H2 temperature-programmed reduction were conducted to characterize the structure and physico-chemical properties of catalysts, which were affected by calcination in the range of 200-600°C. Results show that all the ferrites were with spinel structure, and those calcinated in the range of 300-600°C were in the phase of maghemite. The calcination changed the valence and distribution of Mn and Fe on the ferrite surface, and accordingly the reducibility of ferrites. The HCHO catalytic oxidation test showed that with the increase of calcination temperature, the activity was initially improved until 400°C, but then decreased. The variation of HCHO conversion performance was well positively correlated to the variation of reduction temperature of surface Mn(4+) species. The remarkable effect of calcination on the catalytic activity of Mn-doped spinel ferrites for HCHO oxidation was discussed in view of reaction mechanism and variations in cationic microstructure of Mn-doped ferrites.

Morphology controllable syntheses of micro- and nano-iron pyrite mono- and poly-crystals: a review

Synthesis of iron pyrite with defined morphology has long been actively pursued, due to the strong size and shape dependence of their chemical and physical properties. This review provides comprehensive information outlining current knowledge regarding the morphology controllable syntheses of micro- and nano-iron pyrite mono- and poly-crystals. The wet-chemical methods are summarized as the controllable syntheses, including the hydrothermal, solvothermal, hot-injection and heating-up methods, sulphidation and methods with other relatively high efficiencies. The present study reveals the discussion of relationship between the morphologies and major controlling factors, the temperature, precursor chemicals, solvents and surfactants. The existing challenges for future fine tuning of iron pyrite facets are also proposed for improving the performance of iron pyrite based materials.

Ag3PO4 immobilized on hydroxy-metal pillared montmorillonite for the visible light driven degradation of acid red 18

This work reports the facile fabrication of Ag3PO4/Fe–Al/Mt and Ag3PO4/Al/Mt by loading Ag3PO4 on hydroxy-iron–aluminum pillared montmorillonite (Fe–Al/Mt) and hydroxy-aluminum pillared montmorillonite (Al/Mt). The structural characteristics of the resulting materials were studied with XRD, SEM-EDS, XPS, ICP, nitrogen adsorption–desorption isotherms, and UV-vis diffuse reflectance spectra; the photocatalytic activity of the obtained catalysts was tested using acid red 18 (AR18) as a model contaminant under visible light irradiation. The obtained results illustrate that Ag3PO4 of a high dispersity and smaller size was successfully loaded on hydroxy-metal pillared montmorillonite. The photocatalytic activity and structural stability of the three synthesized catalysts were in the order Ag3PO4/Fe–Al/Mt > Ag3PO4/Al/Mt > Ag3PO4. An efficiency of 98.5% was achieved for AR18 degradation by Ag3PO4/Fe–Al/Mt after recycling seven times, while only 54.9% was achieved for Ag3PO4. The superoxide radical anion (O2˙−) was confirmed to be the dominant reactive species in all the three degradation systems, and the Ag3PO4/Fe–Al/Mt system formed the largest amount of O2˙−. Except for the larger specific surface area and smaller particle size, the high removal efficiency of AR18, remarkable O2˙− generation performance, and good stability of Ag3PO4/Fe–Al/Mt could be attributed to the presence of Fe3+ as well, which can act as an electron acceptor for photo-induced electrons from Ag3PO4 during the photocatalytic process and then inhibit the transformation of Ag+ into metallic Ag.

Natural Magnetite: an efficient catalyst for the degradation of organic contaminant

Iron (hydr)oxides are ubiquitous earth materials that have high adsorption capacities for toxic elements and degradation ability towards organic contaminants. Many studies have investigated the reactivity of synthetic magnetite, while little is known about natural magnetite. Here, we first report the reactivity of natural magnetites with a variety of elemental impurities for catalyzing the decomposition of H2O2 to produce hydroxyl free radicals (•OH) and the consequent degradation of p-nitrophenol (p-NP). We observed that these natural magnetites show higher catalytic performance than that of the synthetic pure magnetite. The catalytic ability of natural magnetite with high phase purity depends on the surface site density while that for the magnetites with exsolutions relies on the mineralogical nature of the exsolved phases. The pleonaste exsolution can promote the generation of •OH and the consequent degradation of p-NP; the ilmenite exsolution has little effect on the decomposition of H2O2, but can increase the adsorption of p-NP on magnetite. Our results imply that natural magnetite is an efficient catalyst for the degradation of organic contaminants in nature.