Fabrication And Photocatalytic Performance Of Intercalated ZnAl-Layered-Double-Hydroxide-Based Composites

On the fact of the increasing environmental contamination, semiconductor-basedphotocatalysis has attracted considerable attention in the photocatalytic degradationof organic pollutants. However, some factors severely hinder the development of thesemiconductor photocatalysis and its applications, such as low solar energy utilizationand low quantum yield. It is noteworthy that heterojunctions fabricated by the layeredcompounds and their suitable semiconductor pillars not only overlay spectralresponse range, but also raise the photocatalytic efficiency by reducing therecombination possibility of the photogenerated carriers.In this dissertation, ZnAl-LDH, a hydrotalcite layered compounds with a highphotocatalytic activity, has been used to prepare modified nanocmoposites. Thenanocmoposites have been prepared using2D ZnAl-LDH nanosheets with0Dphospotungstic acid anion, cadmium sulfide nanoparticle and negatively charged2Dtrititanate nanosheets as building blocks via an exfoliation-restacking route. Theas-prepared cmoposites were investigated by XRD, SEM, UV-Vis DRS, XPS, N2adsorption-desorption isotherms and other technologies. Their photocatalyticactivities were evaluated as well.Firstly, the action of formamide can exfoliate ZnAl-LDH into colloidalunilamellar sheets with positively charge. Mesoporous ZnAl–PW11O39pillarednanocmoposite was prepared by assembling ZnAl-LDH nanosheets with H3PW12O40via an exfoliation-restacking route. Its gallery heights was about0.9nm, and itsspecific surface areas was23m2/g with an average pore diameters of about4.0nm.The results from the photoelectrochemical properties and XPS suggested thatZnAl–PW11O39can efficiently degrade MB molecules under UV-light irradiation as aresult of the synergistic effect between the host and the guest and the high specificsurface area.Secondly, the exfoliated ZnAl-LDH nanosheets were reassembled intoZnAl–CdS pillared composite in the presence of CdS sol. Its pillar height was determined to be about1.6nm, the specific surface46m2/g and the average pore size3.8nm. The photocatalytic activity tests demonstrated that ZnAl–CdS pillarednanocomposite can efficiently degrade MV molecules under visible-light irradiationand that the pillared material exhibited a good stability and an excellent repeatability.Finally, derived from the electrostatic interaction, a new interstratifiednanohybrid ZnAl–Ti3O7has been successfully prepared using the positively chargedZnAl-LDH nanosheets and the negatively charged trititanate nanosheets as2Dbuilding blocks. In the as-prepared nanohybrid, the two kinds of nanosheets arerestacked in a layer-by-layer ordered arrangement at the molecular level. The formedheterojunction provides an effectual spatial separation way to reduce therecombination possibility of the photogenerated carriers. Hence, ZnAl–Ti3O7nanohybrid shows an excellent photocatalytic activity. After120min exposure,99.3%of MB molecules were degraded under UV light irradiation.