Water vapor adsorption and photocatalytic pollutant degradation with TiO2–sepiolite nanocomposites

A new nanocomposite containing a titanium dioxide photocatalyst and low-cost sepiolite was prepared and tested for its potential multifunctional application in water vapor adsorption and pollutant photodegradation. The nanocomposite was characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), thermogravimetric and differential thermogravimetric analyses (TGA/DTG), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) and surface area (BET) measurements. The XRD patterns of the nanocomposites exhibited the characteristic sepiolite and anatase reflections, while the SEM images revealed the surface morphology of the raw sepiolite after the modification with the sol gel prepared with TiO2. In the TGA/DTG, up to 100 °C, three stages of water removal were analyzed and attributed to surface and zeolitic water loss. Upon TiO2 loading, the overall mass loss of sepiolite was reduced to half, but the three stages of water loss were rearranged with low loading (10 wt.%) or were reduced to two stages with higher loading (20 wt.%). The hydrophilic nature of the raw sepiolite was retained after the TiO2 loading, while the water vapor uptake was reduced to 20–30% with relative humidities from 30 to 80% and loadings up to 20 wt.%. In addition, the efficiencies of the supported photocatalysts were investigated using β-naphthol as a model pollutant compound. All prepared catalysts exhibited higher activities than when using the bare TiO2 sample. Therefore, the TiO2–sepiolite nanocomposite can be potentially applied for combined photocatalytic degradation processes and water vapor adsorption to allow for evaporative cooling.

Research Highlights
► The sepiolite structure is not changed with the TiO2 modification in its anatase form.
► The TiO2–sepiolite nanocomposite is hydrophilic with a high water vapor capacity.
► β-Naphthol photodegradations with the supported catalysts are better than with pure TiO2.