Nano-sized Reduced Tungsten/Molybdenum Oxide-based Photocatalysts:Synthesis,Full-spectrum-responsive Photocatalytic Activities And Their Mechanisms

For the recent decades,the efficient use of abundant,clean solar photocatalytic degradation of organic pollutants to treat wastewater has been one of the focused issues by the global researcher,but the photocatalysts that mainly use ultraviolet or visible light have been extensively-investigated while the high-performance photocatalysts which are responsive to near-infrared light?52%of the sunlight energy?are very rare.Therefore,exploring the superior full-spectrum-responsive photocatalysts from UV,visible to near-infrared region ultraviolet?UV/Vis/NIR?has been a great challenge in the field of the current environmental photocatalysis.In addition,although the remarkable photothermal effect of the full-spectrum photocatalysts due to the absorption of NIR light in the sunlight,the influence of temperature on their removal performance of organic pollutants has never been studied.Aiming at discovering and preparing efficient photocatalysts with full spectrum activity from UV,Vis to NIR region,in this paper,based on the topochemical thermal reduction reaction between WO₃·2H₂O nanosheets derived from a mechanochemical approach and alkali carbonate,the K_0.2M_xWO₃?M=Li,Na?were fabricated,and MoO₂/N-doped reduced graphene oxide naonhybrid?MoO₂/N-rGO?was synthesized for the first time via a solution combustion route and subsequent thermal reduction.The full spectrum activities of the two kinds of photocatalysts during the photodegradation of the RhB solution were also studied systematically.Finally,the effect of M ion amount and treated-solution temperature on their removal capacities and the possible photocatalytic mechanisms were dealt with.The results reveal that K_0.2M_xWO₃?M=Li,Na?exhibit superior full-spectrum photocatalytic activities from UV,Vis to NIR region during photodegradation of the RhB.With the addition of M ions into K_0.2M_xWO₃?M=Li,Na?,their photocatalytic activities under UV/Vis/NIR irradiation are enhanced significantly,with the maximum at X=0.3,which can be ascribed to the formation of K_0.3WO₃ and M₂W₂O₇heterostructure in the K_0.2M_0.3WO₃?confirmed by XRD analysis?and enhancement of their photocatalytic activity.Irradiated separately by UV,Vis and NIR light,K_0.2Li_0.3WO₃ can remove 95.1%,94%and 92.2%of RhB from the treated solution within 180min.With excellent UV/Vis/NIR responsive photocatalytic activity and stability of NIR-responsive photocatalytic activity,MoO₂/N-rGO can remove 93.4%,91.7%and 92.7%of RhB respectively from the treated solution under the irradiation of UV,Vis and NIR light within120 min,far higher than 58.7%,32.8%and 29.6%in the case of MoO₂.In the hybrid,N-rGO enhance light absorption ability and effectively inhibit the recombination of photoelectrons and holes in the MoO₂.MoO₂/N-rGO can still remove 81.9%RhB from the treated solution after 5 cycles under NIR irradiation.Studies on the influence of temperature display that under the irradiation of UV,Vis and NIR,increasing the temperature of RhB solution is conducive to enhancing the adsorption performance and photocatalytic degradation activities of K_0.2M_0.3WO₃ and MoO₂/N-rGO,and thus accelerating their removal rates of RhB in the solution.The experiments of active free radical scavengers indicate that O₂^·-,·OH and h⁺radicals play an important role in the degradation of RhB by the two sorts of photocatalysts.In summary,this thesis presents two kinds of novel efficient photocatalysts with full solar spectrum activities,which were prepared by two simple methods and reports synergistic enhancement effect of higher temperature on the removal of organic pollutants from water during photodegradation was revealed,which provides valuable data for efficient photocatalytic removal of organic pollutants by full-spectrum responsive photocatalysts under solar irradiation and full use of photothermal effect.