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Mn-doped Zn/Al layered double hydroxides as photocatalysts for the 4-chlorophenol photodegradation

Morales-Mendoza, G.,Tzompantzi, F.,Garcia-Mendoza, C.,Lopez, R.,De la Luz, V.,Lee, S.W.,Kim, T.H.,Torres-Martinez, L.M.,Gomez, R. Elsevier 2015 Applied clay science Vol.118 No.-
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Mn-doped Zn/Al layered double hydroxides (LDH) with Mn 0.5-3.0% mol respect to Zn content with improved photocatalytic degradation of 4-chlorophenol (4Clphenol) were studied. The characterization studies showed the isomorphic incorporation Mn as dopant until 1% mol. The 4Clphenol degradation was proposed as result of a combined effect of oxidation by both hydroxyl radicals (OH?) and photogenerated holes (h+). In a proposed mechanism it is suggested that Mn enhances the charge separation acting as electron e- (Mn3+; Mn4+) or hole h+ (Mn2+; Mn3+) traps according to its oxidation state. Exhaustive characterization through EDS, XRD, UV-vis-DRS, TEM-Dark field STEM, fluorescence spectroscopy for OH? detection and XPS, has been done denoting the importance of the Mn content and its different oxidation states in the photophysical and photocatalytic properties of the Mn-doped Zn/Al-based layered double hydroxides.
2
Combination of Mn oxidation states improves the photocatalytic degradation of phenol with ZnAl LDH materials without a source of O2 in the reaction system

Morales-Mendoza, Getsemani,Alvarez-Lemus, Mayra,Ló,pez, Rosendo,Tzompantzi, Francisco,Adhikari, Rajesh,Lee, Soo Wohn,Torres-Martí,nez, Leticia M.,Gó,mez, Ricardo Elsevier 2016 CATALYSIS TODAY - Vol.266 No.-
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Abstract Mn-doped Zn/Al layered double hydroxides (LDH) materials were synthesized by the co-precipitation method. X-ray diffraction (XRD) analysis confirmed the polytype structure of LDH materials obtained as well as the successful incorporation of Mn into the structure. Atomic absorption spectroscopy (AAS) and energy dispersive X-ray spectroscopy (EDS) studies showed a well dispersion of Mn and a good correlation between the nominal and experimental composition. Scanning electron microscopy (SEM) revealed the formation of grains close to 1μm length. Energy band gap (Eg) of the solids determined by UV–vis diffuse reflectance spectroscopy (DRS) showed high photoresponse in the ultraviolet (UV) region, which was increased with Mn incorporation into the LDH structure. The LDH materials were evaluated in the photocatalytic degradation of phenol in aqueous medium, under UV radiation with and without O2 source in the reaction system. The results showed that the O2 is not an effective electron scavenger as usually occurs in TiO2 photocatalyst. The Mn effect in the photocatalytic activity was notably marked in anaerobic condition however in aerobic or anaerobic conditions the presence of Mn increases the photoactivity. The phenol mineralization reached in anaerobic conditions was 95% (1.5ppm) of the initial concentration (30ppm) and it is maintained constant after 6h of radiation while in aerobic conditions the TOC reaches only 55% (13.5ppm). The role of Mn as charges separator is discussed and a suitable mechanism is proposed. This study shows that the Mn doped-Zn/Al LDH materials could be a promising photocatalysts under anaerobic conditions for the removal of phenol from aqueous medium. Highlights <UL> <LI> ZnAl LDH rebuilt in phenol solution have not capacity to open the interlayer space. </LI> <LI> A source of O2 have not influence in the phenol photooxidation with ZnAl LDH. </LI> <LI> Mn doped-ZnAl LDH increases the optical properties of absorption. </LI> <LI> The role as electron and hole trap of Mn takes advantage to separate charge. </LI> <LI> The Mn incorporation in ZnAl LDH materials improves the photocatalytic activity. </LI> </UL> Graphical abstract [DISPLAY OMISSION]

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