Synthesis Of Shell-based Photocatalytic Materials And Their Indoor VOCs Purification Performance

In recent years,atmospheric pollution,building and decoration materials pollution made people suffer from the harm of indoor VOCs pollution.However,compared to atmospheric pollution,indoor air pollution received less attention.As people spend more and more time indoors,effective control of indoor VOCs has become a research hotspot in the field of indoor air purification.In addition,with the rapid development of marine shellfish breeding industry in China,shell waste pollution directly affected the quality of people’s life.The decomposition products of it can cause foul smell and water and soil pollution.The problem of shell waste pollution has become an urgent environmental problem.Sufficient investigation of the above two problems showed that photocatalytic technology has great potential in removing indoor VOCs pollution,and the physical and chemical properties of seashell make it possible to replace the high-purity chemical reagents s as multi-functional materials to improve the photocatalytic performance of common catalysts such as Ti O₂ and Mn O_x.In this paper,high performance photocatalyst was synthesized using seashell waste to solve indoor VOCs pollution under visible light.The mechanisms of catalyst synthesis and reaction were investigated.The specific research contents were as follows:（1）Scallop,oyster,clam,mussel,razor clam,and abalone shells were tested as supports for Ti O₂-photocatalyst.The calcined abalone shells（CAS）were found to function as the best support for Ti O₂.Calcined abalone shell with a Ti O₂ loading of23.4%led to a significant improvement in optical absorption.The Na,Sr,S present in the calcined abalone shell were doped into the substitutional sites of Ti O₂and were indispensable to achieve the desired band-gap narrowing and photocatalytic performance;moreover,the Ti and Zn oxides in the calcined abalone shell acted assemiconductors and improved the charge separation efficiency of Ti O₂.（2）Using abalone,scallop,mussel,clam,razor clam and oyster shell as modification materials to synthesize Mn O_x-photocatalyst.In this experiment,carbonized abalone shell powder was found to be the optimal support for Mn O_x（MCA）.MCA exhibited the highest photocatalytic oxidation performance,achieving near 99%degradation efficiency of indoor formaldehyde.It was found that different shells had huge variations in the elementary composition and morphology of crystals.This phenomenon made Mn O_x which was grown in-stiu on the surface of shells have different morphology,and therefore affecting the photocatalytic oxidation performance of the catalysts.（3）An efficient N,Ca co-doped TiO₂ photocatalyst was synthesized by using the insoluble matrix proteins extracted from abalone shell.TIMP-0.8 achieved near completely degradation CH₂O within 45 min under visible light at ambient temperature and exhibited superior stability after 7 cycles.TIMP-0.8 had monodispersity with smaller diameter,high porosity,abundant defects and high adsorption affinity for surface hydroxyls compared with pure Ti O₂.With the assistance of IMPs,the rate-determining step of CH₂O degradation changed from-COOH oxidation to spontaneous decomposition of-HCO₃^-,significantly facilitating the elimination and mineralization of CH₂O.（4）The periostracum layer were used to synthesize the catalyst with visible light response for toluene degradation.The study found that when the initial relative humidity was 45%,the removal rate of toluene on TPAL-1.0 reached 100%.However,the effect of humidity was not great,TPAL-1.0 had high toluene removal rate within the scope of Chinese indoor air quality standards.The high photocatalytic activity of TPAL-1.0 was attributed to the fact that a variety of trace elements such as N,P,Fe and Cu were successfully doped into the Ti O₂ lattice,resulting in abundant defects and high adsorption affinity for surface hydroxyl groups.（5）Natural proteins from waste shell were used as the carbon source and template to synthesize the ternary Ti O₂/C/Mn O₂ photocatalysts.It exhibited high adsorption selectivity and excellent photocatalytic performance for CH₂O and C₇H₈ mixture mineralization under visible light irradiation.The optimal candidate achieved near completely mineralization within 60 min in the simulated indoor environment and exhibited remarkable stability.Large amounts of oxygen vacancies,lattice distortions of Ti O₂,and tailored bandgap structure contributed to these excellent behaviors.Besides,carbon existence as an electron transfer channel dropped the interfacial charge-transfer resistance,thus prolonging the lifetime of charge carriers and making them rapidly go through the surface photo-oxidation reactions.CH₂O and C₇H₈ mixtures possessed the same reaction pathway and rate-determining step with single component.