Surface Modification Of TiO₂ Films With Highly Active Facets For Photocatalytic Degradation Of Micro-organic Contaminants

With micro-organic contaminants?MCs?frequently detected in water sources and indoor air in China and around the world,MCs pollution has become a global environmental problem,and it is urgent to develop economical and efficient MCs purification materials.In this paper,in order to overcome the mass transfer resistance of MCs,based on the preparation of TiO₂ films with high active facets,surface modification with nanopores and Pt single atoms was carried out to investigate the relationship between materials structure and their photocatalytic activity for MCs,so as to develop a kind of highly efficient materials for photocatalytic degradation of MCs.Meanwhile,an innovative vacuum ultraviolet photocatalytic oxidation?VUV-PCO?air purifier was designed and constructed,which promoted the practical application of the materials.The main research contents and results are as follows:?1?TiO₂ film with exposed high active{001}facets and nanopores was fabricated using a one-step hydrothermal method.The effects of pretreatment of the Ti substrate and hydrothermal conditions on the formation of nanopores in the facets of the TiO₂ crystals were investigated.TG/DTA-MS analysis and cleaning and heat treatment of the hydrothermally treated Ti substrate indicate that the presence of residual organic matter and HF in the TiO₂ facets and their transformation and reaction during calcination are essential for nanopores formation on the various facets of the TiO₂ crystals.?2?Photocatalytic degradation of low concentration ethenzamide by nanoporous modified TiO₂ film under UV and VUV irradiation in static and dynamic experiments was studied.Nanoporous TiO₂ film was found to have considerably higher UV photocatalytic activity than non-porous TiO₂ film and P25 coated on the Ti sheet,close to Pt nanoparticles deposited non-porous TiO₂ film when initial ethenzamide concentration was higher than 450 ppb.It exhibited higher activity than Pt nanoparticles deposited non-porous TiO₂ film when initial ethenzamide concentration decreased to 100 ppb.It showed long-term stability within 47 days'continuous dynamic experiments.The nanoporous TiO₂ film still showed significant photocatalytic activity when the concentration of ethenzamide was as low as 15 ppb under VUV irradiation even when the residence time was only 1.8 min.Nanopores play an important role in promoting mass transfer of low concentration ethenzamide,separation of photogenerated carriers and generation of hydroxyl radicals.?3?Photocatalytic degradation of low concentration toluene by nanoporous modified TiO₂ film.The catalytic degradation of toluene at low concentration?25 ppb?was obviously.A VUV-PCO air purifier,consisting of a photocatalytic unit bearing nanoporous TiO₂ film and an ozone removal unit bearing Mn-Fe catalyst,was designed and constructed.The performance of the VUV-PCO air purifier in simultaneous elimination of VOCs and O₃ by-product was evaluated in a sealed actual room.The evaluation was conducted in both intermittent on/off and continuous operations.The results showed that the VUV-PCO air purifier was able to continuously and effectively remove benzene homologues,aldehyde and ketone compounds and O₃ by-product in indoor air,and exhibited good stability.?4?The nanoporous TiO₂ film was further modified by Pt single atoms using impregnation and reduction method.It was found that the concentration of H₂PtCl₆was the key factor affecting the dispersion of Pt single atoms.HAADF-STEM and XAS characterization confirmed that Pt single atoms were dispersed on nanoporous TiO₂ film.When the residence time was 1.8 min and the initial concentration of toluene was 200 ppb,the removal rate of toluene by Pt single atom modified nanoporous TiO2 film reached 45.88%,which was much higher than nanoporous TiO2film and Pt nanoparticles deposited nanoporous TiO₂ film.The photocatalytic efficiency was 5.94 times higher than nanoporous TiO₂ film.When the residence time was only 0.5 min,the removal rate of 500 and 100 ppb ethenzamide reached 94.52%and 100%,respectively,which was 1.90 and 2.07 times higher than that of nanoporous TiO₂ film.It also exhibited good stability in air and water.Pt single atoms can be regarded as an active center and electron capture center of catalytic reaction,and the synergistic interaction with nanopores and highly active facets greatly promotes the photocatalytic degradation of MCs.