Dissociation Adsorption And Dehydrogenation Oxidization Of Formaldehyde On The Surfaces Of TiO₂and Pt Nanocluster

Formaldehyde (HCHO), a colorless and pungent-smelling gas, is considered asthe main indoor air pollutant in modern houses, which easily combines with proteinsin the human body and increases the risks of some diseases including cancer. Thusmany methods, such as adsorption and oxidation, are used to remove HCHO fromair. However, in practical application, the adsorption and oxidation of HCHO bothsuffer from some limitations, such as poor renewability, high cost and low efficiency.The investigation on mechanisms of HCHO adsorption and oxidation can providethe theoretical foundation for the future developments of HCHO adsorbent andcatalyst. TiO2is known for its strong chemical stability, no toxicity, rich source andlow cost, which has been widely used in the purification of indoor air. Hence, thepresent paper is mainly focused on the mechanisms of HCHO adsorption andoxidation on anatase TiO2surface. Those key factors influencing HCHO adsorptionand oxidation are discussed in detail.(1) The F, OH and Cl-modified anatase TiO2nanosheets (TNS) with exposed{001} facets were prepared by a simple hydrothermal and post-treatment method,and their HCHO adsorption performance and mechanism were investigated by theexperimental analysis and theoretical simulations. Our results indicated that theadsorbed F, OH and Cl ions all could weaken the interaction between HCHO andTNS surface, leading to the serious reduction of HCHO adsorption performance ofTNS. However, different from F and Cl ions, OH ion could induce thedissociative adsorption of HCHO by capturing one H atom from HCHO, resulting inthe formation of one formyl group and one H2O-like group. This greatly reduced thetotal energy of HCHO adsorption system. Thus, the adsorbed OH ions couldprovide the additional active centers for HCHO adsorption. As a result, theNaOH-treated TNS showed the best HCHO adsorption performance mainly becauseits surface F was replaced OH. This study will provide new insight into the designand fabrication of high performance adsorbents for removing indoor HCHO and alsowill enhance the understanding of HCHO adsorption mechanism.(2) The mechanism of HCHO oxidation on TiO2surface and Pt nanoclusterwere investigated by density functional theory (DFT). The obtained results showedthat the activation of O2was mainly performed on Pt nanocluster. Especially, the low-coordination Pt atoms in Pt nanocluster were the dominating centers for O2activation. A series of intermediates, such as H2O2, CO,·CHO and·COOH, wereproduced in the process of HCHO oxidation. Though the clean TiO2{001} surfacecannot activate O2and produce available oxidant species, it can use H2O2from Ptnanocluster and adsorbed H2O to oxidize·CHO and·COOH. Besides, thefour-coordination Ti atom in the reconstructed TiO2{001} surface can adsorb andactivate O2. However, the mentioned processes cannot be performed on the TiO2{101} or {100} surface. Hence, TiO2{001} surface can share some non-criticalworks of HCHO oxidation with Pt nanocluster. Thus Pt nanocluster can effectivelyutilize the limited time and space to finish the key works of HCHO oxidization. Thiscan greatly improve the working efficiency of TiO2and Pt nanocluster for HCHOoxidization.