Preparation Of ZnO-based Photocatalysts And Its Application In Marine Oil Pollution

With the development of technology, increasingly marine oils are explored and utilized byhuman beings, thus marine oil pollutions occur unavoidably. Numerous techniques are used tosolve the polluting problems and photocatalytic technique receives much attention for its highefficiency, steady and less secondary pollution. Semiconductor Zinc Oxide(ZnO) is a promisingmaterial with wide direct band gap. In this study, sonochemical precipitation and co-precipitationmethods are employed to prepare pure-ZnO photocatalyst, then changing the properties ofphotocatalysts by barriering the recombination of electron-hole pairs or decresing the band gap.Floating photocatalyst Li/ZnO is synthesized through a coupling agent method and itsphotocatalytic ability is discussed at last. Many influential factors of heterogeneousphotocatalytic degradation of marine oil pollutants are considered, as well as the kinetics. Theresults are as follows.(1) Nano-ZnO particles which are fabricated through sonochemically precipitation methodare characterized by XRD and TEM techniques and the crystal form, morphology and size of theparticles are determined. The photocatalytic ability of as-prepared samples is evaluated throughdiesel pollutants removal experiments under UV lamp using a homemade reactor. The resultsshow that the nano-ZnO is of wurtzite structure and well crystallized, the size of it is around43.3nm; the best reaction condition is: ZnO dosage1.0g/L, diesel initial concentration1.0g/L,pH value7.0, reaction time3h and H2O2concentration0.16%; Under such condition, the bestremoval rate of photocatalytic degradation diesel can reach84%. The influence of each factor onremoving diesel, utilizing range analysis, can be arranged in decreasing order: dosage of ZnO>reaction time> pH value> initial concentration of diesel> concentration of H2O2.(2) Ag/ZnO samples with different doping ratio are synthesized through sonochemicallyprecipitation method, and different kinds of photocatalysts are obtained by changing calcinationtemperature. All the samples are of wurtzite structure with high crystallinity, the size of crystalincreases with Ag doping. The photocatalytic degradation experiments under UV light show thatappropriate Ag doping can improve the photocatalytic ability of photocatalyst in oxiding diesel,and the pH sensitiveness of samples is improved as well. The best reaction condition is: dosageof photocatalyst is2.0g/L, reaction time is2.0h, Ag loading is1.0at%, calcination temperature is400°C and pH value is8.5, in such condition, the best removal rate of photocatalytic degradationdiesel can nearly reach80%. The influence of each factor on removing diesel, utilizing rangeanalysis, can be arranged in decreasing order: raction time> photocatalyst dosage> Ag loading≈pH value> calcination temperature.(3) Pure nano-ZnO photocatalyst is prepared through co-precipitation method, calcination temperature, photocatalyst dosage, diesel initial concentration and pH value are considered inkinetic study. Matching the data with first order reaction and second order reaction, and it isdeemed that nano-ZnO fit second order reaction better.(4) Li/ZnO photocatalysts with various doping ratio are synthesized throughco-precipitation method, and different kinds of photocatalysts are acquired through changingcalcination temperature. It is sure that all the samples are of wurtzite structure and Li element issuccessfully doping into ZnO. With the doping of Li the size of photocatalyst ascendsaccordingly. Photocatalytic capacity of Li/ZnO is superior to that of pure ZnO in removing dieselunder visible light for doping Li can decline the band gap of semiconductor leading to absorbingwavelength red-shift. The best reaction condition is: dosage of photocatalyst2.5g/L, Li loading1.0at%, calcination temperature900°C, diesel initial concentration1.5g/L and pH value8.25,Under such condition, the best removal rate of photocatalytic degradation diesel can reach77%.The influence of each factor on removing diesel, utilizing range analysis, can be arranged indecreasing order: calcination temperature> Li loading≈pH value> diesel initial concentration>photocatalyst dosage.(5)3at%Li/ZnO and pure ZnO fabricated by co-precipitation,1at%Ag/ZnO and pure ZnOsynthesized by sonochemical precipitation are employed to degradation diesel under sunlight andthe result reveals that the photocatalytic abilities can be ranked in decreasing order:3at%Li/ZnOby co-precipitation> pure ZnO by co-precipitation≈1at%Ag/ZnO by sonochemialprecipitation> pure ZnO by sonochemical precipitation. Polypropylene polyhedral ball bondingphotocatalyst is prepared through coupling agent method, and diesel removal rate can up to65%under sunlight after8h reaction, in addition, crude oil removal rate can reach58%in sunshineafter8h reaction.