Synthesis Of Graphene/Tourmaline/TiO₂ Composites And Their Photocatalyic Activity For Photodegradation Of 2-Propanol

Photocatalysis using semiconductor and solar light is regarded as one of the ideal green technologies in dealing with the global energy crisis and environmental issues.The photocatalytic efficiency is influenced by many factors,among which the separation and transportation of photoexcited charge carriers play a crucial role.Previous studies have shown that constructing a composite semiconducting material system is favorable way to an effectively separate the charge carriers.Therefore,we propose a novel graphene/tourmaline/Ti O2 ternary composite photocatalytic materials system.In the composite system,Ti O2 is well known as a typical widely used photocatalyst due to its low cost,non-toxicity,and anti-photocorrosion;graphene is an excellent catalyst support since it has superior conductivity,good electron mobility and very large surface area.More interestingly,tourmaline is a natural mineral,the surface of which exists an electrostatic field.The strong electric field is supposed to play an important role in the separation/transportation of photoexcited charge carriers.In this thesis,we fabricate the grapheme/tourmaline/Ti O2 composite,and systematically investigate the influences of surface electrical property of graphene,surface polarization property of tourmaline,the relative ratios of compoments on the photocatalytic performance of the composite system.Corresponding photophysical and photochemical mechanisms are revealed.A hydrothermal method was employed to synthesize the graphene/tourmaline/Ti O2 composites and compare the effect of surface electrical property of grapene on the performance of composite.GO was prepared from natural graphite powder using a modified Hummers method with negatively charge.GO was modified by poly(diallyldimethylammonium chloride)with positively charge.The results of XRD indicate that Ti O2 in the ternary composite was crystallized in anatase phase,and its crystallinity was not affected by the presence of graphene and tourmaline.No characterisitic peaks for graphene and tourmaline were observed due to their low amounts in composite.TEM observation showed that Ti O2 nanoparticles were uniformly loaded on graphene/tourmaline support.Raman spectroscopy proved that the graphite oxide was reduced to graphene in hydrothermal process.The FTIR and zeta potential measurement demonstrated that the PDDA has successfullymodified graphene oxide.UV-visible diffuse reflectance spectra showed the absorption edge of the composite was identical to that of pure Ti O2,irrespective of the introduction of graphene/tourmaline.The surface area of the composite was measured to be ?160 m2/g,which was almost the same as that of pure Ti O2.The tests demonstrated that the synergetic effect from tourmaline and graphene renders advantageous photocatalytic performance of the graphene/tourmaline/Ti O2 ternary composite over pure Ti O2,Ti O2/tourmaline,and Ti O2/grapheme,the sample containing 0.5 wt% graphene(G0.5)and 5 wt% tourmaline(T5)showed the highest acetone evolution rate of ? 223 ?mol/h.In addition,the effect of surface electrical property of grapene on the performance of composite was also studied.It was found that the negatively-charged-graphene-based composite shown high photocatalytic activity,because the synergetic effect of tourmaline and graphene facilitates separation and transportation of the electrons and holes photogenerated in Ti O2,which is supported by the photoluminescence(PL)intensity.Photocatalytic degradation of IPA over the G0.5/T5/Ti O2 composite using different sacrificial reagents demonstrated that O2·-radicals and holes were the main reactive oxidation species.On the basis of experimental results and theoretical analysis,we propose the reaction mechanism for photocatalytic degradation of IPA over the graphene/tourmaline/Ti O2 ternary composite.