Degradation Of Low Concentration VOCs By Activated Semi-coke Loaded Visible Photocatalysts

The traditional coal chemical industry produces a large amount of semi-coke residue,which,if not put to good use,will not only cause a waste of resources,but also cause a series of environmental problems as a solid waste.Volatile Organic Compounds（VOCs）are produced in various chemical industries（petroleum,coal,organic synthesis,etc.）,which not only cause serious environmental hazards but also affect people’s health.The preparation of activated semi-coke（SAC）with adsorption capacity of VOCs from solid waste semi-coke as raw material and then loaded with visible light catalyst to degrade VOCs can achieve the purpose of"treating waste with waste",which can save resources and achieve a clean and friendly environment.By loading visible photocatalysts on the active semifocus,the problems of short residence time of gases on the material surface,few active sites and high complexation rate of photogenerated electron-hole pairs and slow carrier transport efficiency can be effectively solved to enhance the synergistic effect of adsorption-photocatalysis and realize the efficient degradation of VOCs.The core of adsorption-photocatalytic technology is the research and development of composite materials,mainly including the preparation and modification of active semi-focal substrates and the selection and modification of photocatalysts.Reactive semi-coke is a kind of carbon material with high specific surface area,high porosity,strong electrical conductivity,rich surface functional groups and strong adsorption capacity,which can be used as an excellent support substrate for adsorption-photocatalytic synergy in the treatment of gas pollutants.Therefore,in this study,SAC was selected as the support substrate on which the visible photocatalyst was loaded,and the photocatalyst was modified by constructing a heterojunction to improve the adsorption-photocatalytic synergy and apply it to the degradation of low-concentration VOCs.This thesis addresses the problems of high photogenerated electron-hole complexation rate,few reaction sites and weak adsorption capacity of VOCs by photocatalysts.The g-C₃N₄-Bi₂WO₆/SAC and Bi VO₄-Bi PO₄-g-C₃N₄/SAC composites were constructed by using SAC as a loading substrate for photocatalysts loaded with binary and ternary Z-Scheme heterojunction photocatalysts with visible light response.The structural composition,morphological characteristics,visible light responsiveness,photogenerated carrier complexation and the synergistic adsorption-photocatalytic effect mechanism were investigated by various characterizations.The catalytic performance of the composites was also evaluated by decomposing representative VOCs such as formaldehyde,benzene and toluene in visible light and the photocatalytic oxidation mechanism was investigated.The following conclusions were drawn from the study.（1）The g-C₃N₄-Bi₂WO₆/SAC（NB/SAC）composites with visible light response were successfully loaded with binary Z-Scheme heterojunction photocatalyst g-C₃N₄-Bi₂WO₆ on SAC by hydrothermal method.It was found that the g-C₃N₄-Bi₂WO₆/SAC（NB/SAC）composites with 50%photocatalyst loading mass fraction had the best visible light response and VOCs degradation effect.50 wt.%NB/SAC material achieved 93.6%,84.4%and 78.8%degradation rates of formaldehyde,benzene and toluene in 130 min,which were higher than those of the single photocatalyst.5.74,4.66 and 4.55 times higher than that of a single photocatalyst.The material was stable,maintaining high degradation performance of 84.8%,79.6%and74.0%even after five cycles.Capture experiments showed that hydroxyl radicals（·OH）and superoxide radicals（·O₂^-）are the main active species in the degradation pathway.In this study,the mechanism of using SAC as a substrate to enhance photocatalytic degradation performance is described.The results of this study provide new ideas for the resourcefulness of solid waste and the effective degradation of VOCs.It also provides a theoretical basis for the development and application of high-performance photocatalysts.（2）In order to further reduce the composite rate of photogenerated carriers in photocatalytic materials and improve the degradation performance of the composites,ternary Z-Scheme heterojunction Bi PO₄-Bi VO₄-g-C₃N₄/SAC（PVCN/SAC）composites were constructed in this paper.The ternary heterojunction photocatalysts exhibited better visible light response and stronger degradation of VOCs as confirmed by test characterization analysis.Based on the synergistic effect of adsorption and photocatalysis,the degradation efficiency of the obtained PVCN/SAC material for toluene can reach 85.6%within 130 minutes under simulated sunlight,which is 2.43times that of the ternary heterojunction photocatalyst before loading,and the degradation rate of toluene is 4.43 times higher than that of a single photocatalyst.Compared with SAC-supported binary photocatalysts,the efficiency of toluene degradation of composites supported with ternary heterojunction photocatalysts is improved.Capture experiments show that superoxide radicals（·O₂^-）and hydroxyl radicals（·OH）are the key active species in the degradation pathway.Even after five cycles,the material maintained 81.6%degradation performance.This study provides new ideas for the efficient and stable degradation of VOCs and the design of photocatalysts.