Graphene modified “black {0 0 1}TiO₂” nanosheets for photocatalytic oxidation of ethylene: The implications of chemical surface characteristics in the reaction mechanism

In this work, crystal facets, bandgap, size and shape of reduced graphene oxide (rGO) modified anatase {0 0 1} black TiO₂ nanosheets (rGO-B-TiO₂ NSTs) were tailored for the photocatalytic oxidation of ethylene under high humidity content. XRD, Raman and HR-TEM analyses confirm that rGO-B-TiO₂ NSTs have a 94 % of exposed {0 0 1} facets with high number of oxygen vacancies. In addition, rGO-B-TiO₂ NSTs exhibit increased values of surface area and porosity compared to its pristine form. A 48 and 34 μmol g⁻¹ of ethylene are adsorbed at the surface of rGO-B-TiO₂ NSTs in the absence and in the presence of humidity, respectively. In addition, operando DRIFTS analyses provide the insight of surface interactions between ethylene molecules and adsorption sites of rGO-B-TiO₂ NSTs. The photocatalytic removal efficiencies of the synthesized materials under both UV and visible light irradiation proceed as follows: rGO-B-TiO₂ NSTs > B-TiO₂ NSTs > TiO₂ NSTs > commercial TiO₂ NPs. Further, ethylene is very quickly photocatalytic oxidized when rGO-B-TiO₂ NSTs is applied under UV light irradiation, having a 72 and 92 % ethylene removal in the absence and in the presence of humidity, respectively. Moreover, a 48 and 58 % of ethylene removal takes place in the absence and presence of humidity under visible light irradiation, respectively. Results indicate that rGO-B-TiO₂ NSTs boost the photocatalytic activity through their virtue of visible-light absorption properties (Bandgap = 2.61 eV) and the rapid electron-hole separation at the rGO {0 0 1} black TiO₂ NSTs interfaces. Such findings are confirmed through UV-visible diffused reflectance, photoelectrochemical and photoluminescence analyses. Nanosheets made of rGO modified {0 0 1} black TiO₂ could be used as an effective photocatalyst for the removal of ethylene from large volume fruit storage areas by exploiting a simple light source in the presence of high content of humidity.