Plasma-assisted Preparation Of Hydrotalcite-like Material And Study On Its Photocatalytic Properties

Energy and environmental issues are two important issues that we are facing today.Using sunlight to drive the photocatalytic oxidation reaction to achieve the degradation of pollutants provides a solution to two major problems.Semiconductor-based photocatalysts have been widely used.However,the wider forbidden band width and the higher photogenerated electron-hole recombination rate make it impossible to achieve efficient use of solar energy.Layered double hydroxides?LDHs?have a layered,plate-like porous structure,which facilitates the transfer of photogenerated electrons and makes it an excellent photocatalyst.The chemical composition of LDHs laminates is adjustable.Adding specific metal elements can obtain hydrotalcite photocatalyst with good photoresponse.Dielectric barrier discharge low temperature plasma technology is used in the preparation and synthesis of materials,which can reduce the particle size and increase the specific surface area.It is a new method to improve the photocatalytic performance of hydrotalcite materials.In this paper,ZnCuFeCr hydrotalcite?ZnCuFeCr-LDHs?materials were prepared by co-precipitation method and low-temperature plasma-assisted method,and modified with surfactant.The performance of ZnCuFeCr-LDHs photocatalytic degradation of methyl orange wastewater was studied.Firstly,ZnCuFeCr-LDHs were synthesized by co-precipitation method.The photocatalytic degradation performance of hydrotalcite with different metal element ratio was investigated.ZnCuFeCr-LDHs had the best photocatalytic degradation performance when the ratio of elements was M²⁺/M³⁺=3,Zn²⁺/Cu²⁺=1,Cr³⁺/Fe³⁺=0.2.The degradation rate of 1 L methyl orange solution?80 mg/L?reached 99.5%when irradiated with UV light for 30 min.The degradation rate of 1 L methyl orange solution?20 mg/L?was 46.1%when exposed to visible light for 72 min.The element ratio affected the Light responsiveness and photocatalytic performance.ZnCuFeCr-LDHs with element ratio M²⁺/M³⁺=3,Zn²⁺/Cu²⁺=1 and Cr³⁺/Fe³⁺=0.2were prepared assisted with dielectric barrier discharge low temperature plasma.The effect of discharge voltage and discharge time was studied.The degradation rate of methyl orange was 98.3%when irradiated with UV light for 18 min using sample prepared with discharge voltage of 30.9 kV and discharge time of 4 h.The degradation rate of methyl orange was 96.8%under visible light irradiation of 42 min using samples prepared with discharge voltage of 30.9 kV and discharge time of 3 h.The plasma-assisted preparation method was a simple and effective preparation method of hydrotalcite,which could effectively shorten the preparation time of the photocatalyst and improve the degradation efficiency.Cetyltrimethylammonium bromide?CTMAB?,sodium dodecyl benzene sulfonate?SDBS?and polyethylene glycol?PEG?were added separately to prepare ZnCuFeCr-LDHs.The effects of the type and amount of surfactant,discharge voltage and discharge time on the photocatalytic degradation performance were studied.The effects of catalyst addition,pH,salt effect,and H₂O₂ on the photocatalytic performance during degradation process were also investigated.For the samples with CTMAB addition amount of 1 mmol/L,discharge voltage of 30.9 kV and discharge time of 3 h,the adsorption degradation rate in the dark treatment stage was 58.5%.The photocatalytic degradation rate of 1 L methyl orange solution?20 mg/L?was 40.7%and the final degradation rate was 99.2%after 42 min of visible light irradiation.The optimal amount of catalyst added during the reaction was 1 g/L.The optimal pH of the reaction solution was 6.Na₂SO₄ could inhibit the photodegradation effect.H₂O₂ could promote the photocatalytic degradation effect to a certain extent.Therefore,adding a certain amount of CTMAB could effectively improve the adsorption and degradation performance of ZnCuFeCr-LDHs,but it would weaken its photocatalytic degradation performance.