Study On Hydrothermal Synthesis Of Hollow Structured Cu₂O Micro/Nano-spheres And Their Applications On Lithium Storage And Dye Removal

Micro/nano-structured transition metal oxides semiconductors with porousand/or hollow structures have been heavily involved in newly developed energystorage and conversion systems. Moreover, many metal oxide semiconductors can beused as photocatalysts to degrade organic dyes in wastewater by the pairs of electronsand holes, which are directly generated under visible light irradiation. In the lastdecades, plenty of these materials have been synthesized and some of them have beenused in the applications of lithium ion batteries (LIBs) and photo-degradation. Amongthe large number of transition metal oxide semiconductors, cuprous oxide (Cu2O), ap-type semiconductor with a direct band gap of2.17eV, has received much attentionin widespread potential applications for LIBs, photo-degradation and otherapplications due to its low cost and environmentally friendly features. In this thesis,we introduce a facile hydrothermal route to prepare hollow structured Cu2Omicro/nano-spheres with enhanced performances in LIBs and dye removal(adsorption and photodegradation).Generally, synthesis of pure metal oxides with a hydrothermal method lasts fromseveral to dozens of hours. Herein, we introduce a very simple one-pot template-free“short time hydrothermal” synthesis approach to prepare hollow structured Cu2Omicrospheres. The copper nitrate trihydrate (Cu(NO3)2·3H2O) is used as precursor andwater (H2O)/ethylene glycol (EG) plays as a solvent in the reaction system, withoutany additional additives or template-agent. Under this reaction system, pure Cu2Ocrystals could be obtained in only1h (even15min). The hollow structured Cu2Omicrospheres with a controllable diameter (0.5to4.2μm) could be easily obtained byadjusting the H2O volume in the reaction system. Based on the approach mentionedabove, we designed a new approach to synthesize the hollow structured Cu2Onanospheres. Without water addition, the hollow Cu2O nanospheres with controllablediameters (125to210nm) could be obtained. Our results reveal that the {110} and{111} facets are exposed on the surface of the as-prepared hollow Cu2Omicro/nano-spheres.The lithium storage performance of the Cu2O micro/nano-spheres was investigated, which dilivered that the microspheres with a diamter of1.6μmdisplayed a good cycle stability with a reversible capacity of370mAh/g at a rate of0.2C after200cycles. To the best of our knowledge, the lithium storage capacity andcycle performance are far much better than the previous reported Cu2O electrodes.The reversible specific capacity of the as-synthesized Cu2O nanospheres with adiamater of125nm was534mAh/g at a rate of0.2C, which is considerable higherthan the other pure Cu2O nanostructured electrodes previously reported.The organic-dye removal properties were evaluated by the adsorption andphotocatalytic degradation of methyl orange (MO) aqueous solution. It is important torealize that it is hard to achieve the adsorption-desorption equilibrium in the Cu2Oremoval system due to the strong adsorption effects when we evaluate itsphotocatalytic efficiency. Therefore, a very simple and useful method is employed toevaluate the Cu2O photocatalytic and adsorption efficiencies: the photocatalyticefficiency (Ep) equals to the removal efficiency (Er) minus the adsorption efficiency(Ea), i.e. Ep=Er-Ea. When the Cu2O microshperes with diamaters of0.5,1.6and3.2μm were used as the photocatalysts under visible light irradiation, the removalefficiencies reached to96,96and91%, and the adsorption efficiencies were27,47and42%, respectively. The photocatalytic efficiencies were calculated as69,49and49%, subsequently. For the adsorption performance of the Cu2O nanospheres, thedifferent concentrations with a high level of MO aqueous solution were used. For theMO aqueous solution with concentrations of50,100,200and400mg/L,99.5,99.6,99.3and99.6%of MO were adsorbed after30,60,120and360min, respectively.Moreover, the maximum adsorption amount reached to996.0mg/g in360min. To thebest of our knowledge, these values are the best of all the Cu2O adsorbents atprersent.