Synthesis And Properties Of ZnO/mixed Mg-Al Oxides As A Strongly Adsorptive Photocatalyst

The layered double hydroxides(LDHs) are a group of inorganic layered materials which consisting of brucite-like layers.Because of the well-defined layered structures and special properties of LDHs,these materials attracted increasing interest in the field of material science and they have potential applications in wide areas.In addition,many researches are focusing on the applications of their corresponding mixed metal oxides as adsorbent materials or catalytic materials.However,the applications of the LDHs are limited because the adsorption on adsorbents does not degrade the contaminations and only transfers them from one phase to another.Meanwhile,the LDHs prepared by co-precipitation are with the low specific surface area and the large grain size,and the adsorbing activities are tightly related to the grain size.Thus,the investigations on how to improve the adsorbing activity of LDHs are significative.In this paper,the Mg-Al-CO₃ layered double hydroxides (Mg-Al-CO₃-LDHs) were prepared by the co-precipitation method with the mixture of NaOH and Na₂CO₃ or(NH₄)₂CO₃ as precipitated agent, respectively.The effect of precipitated agents on grain sizes of the Mg-Al-CO₃-LDHs was investigated.The Mg-Al-CO₃-LDHs and the LDHs derived Mg-Al oxides were characterized by X-ray diffraction (XRD),transmission electron microscope(TEM) and Brunauer Emmett Teller procedure(BET).The adsorption of acid red G(ARG) was used as a model dye to evaluate the adsorption abilities of LDHs derived mixed metal oxides.The Mg-Al-CO₃-LDHs were subsequently decorated with ZnO nanorods through a homogeneous precipitation process in order to avoid the secondary pollution in the adsorption process.The decoration of ZnO makes calcined Mg-Al-CO₃-LDHs(cZnO/LDHs),a kind of strong adsorbents for adsorbing anionic dyes,have a photocatalytic activity.They were characterized by XRD,TEM and UV-vis diffuse reflectance spectra(UV-vis DRS).The TEM images illustrate that the morphology of ZnO is a nanorod with a diameter of about 15 nm.In photocatalytic experiments,the degradation of ARG by cZnO/LDHs is efficient, especially the one with the mass ratio of 1:1.In nonirradiated adsorption-photocatalysis experiments,the degradation of ARG by the cZnO/LDHs with the mass ratio of 3:1 is also obvious after saturated adsorption and photocatalysis.In addition,this kind of nanocomposites also has the antibacterial property and the antibacterial ratio is above 99.9%.The mixed Mg/Al oxides were restructured to LDHs by soaking in Na₂CO₃ solution.The best restructured LDHs were restored in the solution with the concentration of 1M for 24 hours.After the restoration, the shape of LDHs changed into the sheet-like structure and their specific surface area also increased from 66.1 m²/g to 224.2m²/g.And the mixed oxides derived from the restructured LDHs have the better adsorption abilities for adsorption of ARG and the time for adsorption is only 30 minutes.