Synthesis Of Modified TiO₂/Diatomite Composite For Adsorption And Photocatalytic Degradation Of Formaldehyde

Semiconductor photo-catalysts, such as nanostructured Ti O2, have been widely employed in the field of medical disinfection and sterilization, domestic and industrial wastewater treatment, functional building coatings, interior decoration materials and solar cells since Ti O2 was found to be a good photocatalyst for the redox of water to generate H2 under the radiation of photo-cell in 1972, where the varied applications of Ti O2 is based on its high catalysis activity, excellent chemical stability, low cost, high security and great potential in degrading organic dying. Diatomite is a natural porous material with abundant nano-sized pores, high BET, excellent chemical stability and superior adsorption capacity, which has been intensively used as suitable matrix materials for loading Ti O2 catalyst. Via the synergetic effect of diatomite and Ti O2, the Ti O2/diatomite compound is expected to be an highly efficient catalyst for the adsorption and degradation of formaldehyde.Herein, different kinds of Ti O2 catalysts, including pure Ti O2, V-doped Ti O2, N-doped Ti O2 and V, N-co-doped Ti O2(defined as Ti O2, V-Ti O2, N-Ti O2, and V-N-Ti O2, respectively) were primarily prepared via a modified sol-gel method, where the optimal doping statutes of Ti O2 were further evaluated. Then, diatomite raw materials were purified to reach level-one national standard of soil through a comprehensive method. Subsequently, the composite materials consisting of diatomite and Ti O2 were fabricated by sol-gel approach. In this work, scanning electron microscope(SEM) and transmission electron microscope(TEM) were used to analyze the morphology of diatomite/Ti O2 composite. The structure of the composite was characterized by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and Fourier transformation infrared spectroscopy(FTIR). Finally, the photocatalytic activity and adsorption-degradation performance of these composites were investigated with UV–vis diffuse reflectance spectrometer(UV-Vis) and adsorption curves of formaldehyde.Anatase-type Ti O2 with various doping statutes, such as pure Ti O2, V-doped Ti O2, N-doped Ti O2 and V, N-co-doped Ti O2, were synthesized via a modified sol-gel method. By analyzing the morphology of these Ti O2 samples, we can conclude that the particle size of Ti O2 after N doping or V doping will dramatically decrease and present an irregular shape, where N-doped Ti O2 deliver a minimum size and the average size of V-doped Ti O2 is ranged between that of pure Ti O2 and N-doped Ti O2; Moreover, the average size of V, N co-doped Ti O2 is similar to that of pure Ti O2. The adsorption capacity of Ti O2 was enhanced after N or V doping which was confirmed by UV-Vis measurement. The comparison of the adsorption capacity towards visible lights for different Ti O2 was evaluated as follows: V-N-Ti O2> V-Ti O2> N-Ti O2>Ti O2. In addition, 0.5% V doping and 15% N doping were separately evaluated to be the best condition for Ti O2 in terms of photocatalytic performance by the degradation measurement of methylene blue.Sieving method, pickling method and calcining method were separately employed to purify the diatomite raw materials, where the optimal sieving mesh number, pickling concentration and calcining temperature were 320, 60%H2SO4 and 550 oC for 3h, respectively. Subsequently, a comprehensive method combining the above-mentioned methods with optimal conditions was used for the final purification of diatomite and the content of Si O2 in the as-obtained samples was calculated to be 89.1%, which agreed with the standard of national level-one soil. Furthermore, the physical adsorption was found to be the main mechanism in adsorbing formaldehyde for diatomite, which presented a regular cycling pattern of adsorption – desorption- adsorption.The final Ti O2/diatomite composite, including Ti O2/DE, 0.5%V-Ti O2/DE, 15%NTi O2/DE and 0.5%V-15%N-Ti O2/DE, was obtained from a modified sol-gel method where Tetrabutyl orthotitanate(TBOT) was used as the precursor followed by mixing them with diatomite during the synthesis of Ti O2. It was confirmed that Ti O2 was uniformly coat on the surface and around the pores of diatomite with SEM and TEM analysis. Another result can be gained from the adsorption curves of formaldehyde that formaldehyde can not only be adsorbed by both pure Ti O2/ diatomite and modified Ti O2/ diatomite composites but also chemically decomposed, and the comparison of the degradation capacity for these composites can be depicted as follows: V-N-Ti O2/DE > N-Ti O2/DE > V-Ti O2/DE > Ti O2/DE. To illustrate, V-N-Ti O2/DE composite, which delivered the highest degradation performance, can reduce the concentration of formaldehyde in the simulation testing chamber from 6.413 mg/m3 to 0.169mg/m3.