Study On The Natural Light Photocatalytic Degradation Of Formaldehyde Composite Humidity-controlling Materials Based On Sulfur Doped G-C₃N₄/TiO₂

Indoor air environment includes indoor heat and humidity environment and indoor air quality,and the indoor formaldehyde concentration which has an important impact on indoor air quality exceeds the standard,which will cause great harm to people’s health,so people pay more attention to it.Formaldehyde can be continuously degraded into harmless CO₂ and H₂O by photocatalytic reaction,which is a low carbon and environmental protection method of formaldehyde reduction.Material researchers are constantly trying to improve its photocatalytic performance.However,the commonly used photocatalyst TiO₂ can produce photocatalytic reaction only under ultraviolet light,and the indoor light environment is mainly natural light.Therefore,it is of great theoretical and practical value to modify the existing photocatalysts and develop photocatalysts that can degrade formaldehyde under natural light.Therefore,on the basis of our team’s previous research on g-C₃N₄-TiO₂（CNT）photocatalyst,this study made efforts in the research and development of photocatalyst to improve the photocatalytic effect under natural light.The research idea is to modify g-C₃N₄ by doping g-C₃N₄（CN）with S to prepare SCN to inhibit the recombination rate of g-C₃N₄ photocarriers.SCN and TiO₂ were compounded to form SCNT photocatalyst by impregnation method,and the optimal ratio of SCN:TiO₂ in SCNT photocatalyst was investigated.The diatomite（sepiolite）/sphagnum humidity-controlling materials with high strength,good water resistance and good moisture control performance was used as the carrier of SCNT photocatalyst to prepare a new photocatalytic composite humidity-controlling materials.The formaldehyde degradation rate,relative humidity and temperature of diatomite（sepiolite）/sphagnum photocatalytic composite humidity-controlling materials supported by SCNT photocatalyst were compared and analyzed through simulated chamber test.On this basis,XRD,ESEM,EDS,FTIR,UV-VIS and PL spectra were used to study the photocatalysis,temperature and humidity regulation mechanism of diatomite（sepiolite）/sphagnum photocatalytic composite humidity-controlling materials.The research results are as follows:（1）SCNT photocatalyst was developed and compared with the existing CNT and TiO₂.The degradation effect of formaldehyde was SCNT（1:1）>CNT>TiO₂.When diatomite/sphagnum and sepiolite/sphagnum were used as the support of photocatalyst,the photocatalytic effect of SCNT photocatalyst with different SCN:TiO₂ mass ratios was SCNT（1:1）>SCNT（1:2）>SCNT（2:1）,that is,SCN:TiO₂ was 1:1 is the best ratio of SCNT photocatalyst.（2）G-SCNT（1:1）and H-SCNT（1:1）photocatalytic composite humidity-controlling materials were prepared using SCNT（1:1）as photocatalyst and diatomite/sphagnum and sepiolite/sphagnum basic humidity-controlling materials as negative carriers of photocatalyst.The results showed that G-SCNT（1:1）photocatalytic composite humidity-controlling materials had better formaldehyde degradation and hygroscopic effect than H-SCNT（1:1）photocatalytic composite humidity-controlling materials.Under natural light,the formaldehyde degradation rates of G-SCNT（1:1）and H-SCNT（1:1）were 65%～81%and 60%～68%in the daytime,and about 80%and 70%at night,respectively.The relative humidity of blank chamber,G-SCNT（1:1）and H-SCNT（1:1）chambers was 45%～73%,52%～69%and 50%～70%,respectively.The two photocatalysts also have a temperature regulating effect of about 1℃.（3）photocatalytic composite humidity-controlling materials have a good catalytic degradation effect on formaldehyde in the daytime.It can not only degrade formaldehyde in the air,but also degrade formaldehyde adsorbed in the humidity-controlling materials.At night,the material can still control the concentration of formaldehyde in the chamber through capillary channel effect and physical and chemical adsorption.The photocatalytic composite humidity-controlling materials can control indoor formaldehyde concentration all day through the synergistic effect of photocatalytic and adsorption.（4）UV-Vis analysis and band gap diagram show that the band gap widths of g-C₃N₄ and SCN are 2.53 e V and 2.42 e V,respectively.The band gap widths of SCNT（1:1）,G-SCNT（1:1）and H-SCNT（1:1）are 2.74 e V,2.30 e V and 2.10 e V,respectively.In other words,the band gap widths of SCNT（1:1）photocatalyst will decrease when the wet materials of diatomite/sphagnum and sepiolite/sphagnum are supported.The photocatalytic effect of SCNT photocatalyst in ultraviolet and visible region was increased.（5）FTIR analysis showed that there were stretching vibration peaks of Si-OH in diatomite and sepiolite.Si-OH could generate acidic sites,effectively capture photogenerated holes（h⁺）,slow down the recombination rate of photogenerated electrons and holes,and provide active adsorption sites,thus enhancing the activity of photocatalytic composite humidity-controlling materials.（6）The analysis by ESEM and EDS showed that the specific surface area of G-SCNT（1:1）photocatalytic composite humidity-controlling materials was larger than that of H-SCNT（1:1）photocatalytic composite humidity-controlling materials,and the pore distribution at nanometer level was more uniform,making its photocatalytic degradation of formaldehyde and temperature and humidity regulation better than H-SCNT（1:1）material.This study is of great significance to the theoretical and applied research of thermal and humid environment and indoor air quality in the control room of photocatalytic composite hygroscopic materials.