Applications Of The Prepared Several New Z-scheme Photocatalysts In Conversions Of Nitrogen And Sulfur Oxide Oxides

As a food additive,nitrite and sulfite are widely used in various fields of food processing.Nitrite is mainly used as a coloring agent,flavoring agent and preservative in food processing,especially in people's favorite preserved foods.However,nitrite has a certain toxicity,and the discharge of wastewater containing excessive nitrite into the water body will cause the metabolic function of aquatic organisms to be dysfunctional,and the immunity will decrease,thereby causing lesions and even death.Sulfite is widely used in food processing because of its various functions of bleaching,antiseptic,anti-oxidation and its low price.However,discharging of wastewater containing excess sulfite into the water body can cause serious damage to the nervous system and respiratory system of aquatic animals.Therefore,the removal of nitrite and sulfite in industrial wastewater is very important to maintain a balanced and stable aquatic ecosystem.Photocatalytic technology with semiconductor materials as the core provides us with a new idea of pollution control.The photocatalytic technology to treat nitrites and sulfites is a green,clean,and effective treatment.Nitrite and sulfite can simultaneously undergo redox reactions in a photocatalytic system.Since nitrite mainly utilizes the reduction of photocatalytic systems,and sulfite mainly utilizes the oxidation of photocatalytic systems,simultaneous treatment of nitrites and sulfites in the same photocatalytic system can mutually promote their respective reactions rate.In recent years,Z-scheme photocatalysts have been widely used in the field of photocatalysis and acoustic catalysis.Z-scheme photocatalysts can have strong oxidizability and strong reducibility at the same time,and can broaden the response range of light.Therefore,the wide band-gap semiconductor NiGa₂O₄ and the relatively narrow band-gap WO₃,BiSn₂O₇ and MoO₃ are respectively formed into a Z-scheme photocatalyst.The key to improve the photocatalytic efficiency of Z-scheme photocatalysts is to enhance the separation efficiency of photogenerated electron-hole pairs.The conventional approach is to add conductive channels such as noble metals.However,the noble metals have narrow and fixed energy levels that may deviate from the conduction band or valence band position of the semiconductor,which is detrimental to the flow of electrons through the precious metal particles.In addition,due to the addition of these precious metals,the operating distance of electrons has also increased.Taking into account the above points,the use of extremely narrow band gap semiconductors as conductive paths,the separation efficiency of photogenerated electron-hole pairs can be greatly enhanced,and the electron flow speed can be accelerated.NiGa₂O₄/NiS₂/WO₃,Er³⁺:Y₃Al₅O₁₂@NiGa₂O₄/?NiS,CoS₂ or MoS₂?/Bi₂Sn₂O₇and NiGa₂O₄/AQ/MoO₃ were prepared and forming three composite solar photocatalytic systems.X-ray diffraction?XRD?,photocurrent response?IT?,electrochemical impedance?EIS?,energy dispersive X-ray spectroscopy?EDX?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray photoelectrons Energy spectrum?XPS?,photoluminescence spectroscopy?PL?,Fourier transform infrared spectroscopy?FT-IR?,UV-visible diffuse reflectance spectroscopy?UV-DRS?and Raman spectroscopy?Raman?were characterized to the surface morphology,crystal type and chemical composition of the above catalyst.In addition,we also evaluated the effects of photocatalyst type,illumination time,electron hole sacrificial agent,pH value and cycle times on simultaneous photocatalytic conversions of NO₂^-and SO₃^2-in three photocatalytic systems.Studies on three photocatalytic systems have shown that nitrites and sulfites can simultaneously undergo redox reactions in the same photocatalytic system and promote each other's reaction processes.The introduction of a narrow-band semiconductor as a conductive channel can solve the problem of the conventional conductive channel and further improves the photocatalytic activity.By comparing the narrow-band semiconductor conductive channels with different bandwidths,the results show that the photocatalytic conversion rate of the conductive channel with the approximate step structure at the energy level is the highest.In addition,the unique chemical and physical properties of the Z-scheme NiGa₂O₄/AQ/MoO₃photocatalyst provide a new electron transfer mode,namely charge transfer,which effectively accelerates the electron transfer rate.This study provides a new way to use sunlight to simultaneously convert nitrite and sulfite or other environmental pollutants.