White and Red Brazilian São Simão’s Kaolinite–TiO2 Nanocomposites as Catalysts for Toluene Photodegradation from Aqueous Solutions

Abstract

The presence of volatile organic compounds in groundwater is a major concern when it is used as a drinking water source because many of these compounds can adversely affect human health. This work reports on the preparation and characterization of white and red Brazilian São Simão’s kaolinite-TiO2 nanocomposites and their use as catalysts in the photochemical degradation of toluene, a significant volatile organic compound. The nanocomposites were prepared by a sol-gel procedure, using titanium bis(triethanolaminate)diisopropoxide as a precursor. Thermal treatments of the nanocomposites led to different polymorphic titania phases, while the clay changed from kaolinite to metakaolinite. This structural evolution strongly affected the photocatalytic degradation behavior—all the solids efficiently degraded toluene and the solid calcined at 400 °C, formed by kaolinite and anatase, showed the best behavior (90% degradation). On extending the photochemical treatment up to 48 h, high mineralization levels were reached. The advantage of photodegradation using the nanocomposites was confirmed by comparing the results from isolated components (titanium dioxide and kaolinite) to observe that the nanocomposites displayed fundamental importance to the photodegradation pathways of toluene.

Titania-triethanolamine-kaolinite nanocomposites as adsorbents and photocatalysts of herbicides

“…After calcination at higher temperatures, the bands in the 3200-3700 cm -1 region disappeared, which evidenced that kaolinite was transformed into metakaolinite, with further appearance of a broad band at 1050 cm -1 , characteristic of SiO 2 . Moreover, the change in the band structure in the 400-1250 cm -1 region originated from the kaolinite → metakaolinite transformation, which modified Al 3+ coordination from octahedral to tetrahedral [25][26][27][28]34,37,38]. The band at 950 cm -1 , assigned to the Si-O-Ti antisymmetric stretching vibration, has been proposed as evidence of nanocomposite formation (Kočí et al, 2011) [39].…”

“…The uses of layered solids to immobilize semiconductors such as titanium dioxide have attracted interest from various researchers on the last years [25][26][27][28][29], all this authors justify the use of layered solids due the increasing of specific surface area, synergistic effect during photodegradation process due the adsorption and photocatalysis enhancement, presence of transition metals that could induces the change of bandgap of semiconductor, and obviously the recyclability ability that are increased using this class of matrix.…”

“…Layered solids have been used to immobilize semiconductors such as titanium dioxide, zinc oxide, and zirconium oxide and have attracted the interest of researchers in the last years [25][26][27][28][29]. The use of layered solids is advantageous because they have large specific surface area; they act synergistically with the semiconductor during photodegradation, thereby enhancing substrate adsorption and photocatalysis; they contain transition metals that could change the bandgap of a semiconductor, and they can be recycled.…”

“…The use of layered solids is advantageous because they have large specific surface area; they act synergistically with the semiconductor during photodegradation, thereby enhancing substrate adsorption and photocatalysis; they contain transition metals that could change the bandgap of a semiconductor, and they can be recycled. The unique structural properties of clay minerals (e.g., specific surface area, cationic exchange capacity, adsorption ability, and swelling property of the smectite group) make them efficient platforms for photocatalytic, catalytic, and adsorption applications [25][26][27][28]. Concerning photocatalytic applications, the use of clay minerals is justified because hydroxyl groups are photocatalytically generated on the surface of particles dispersed on layered or fibrous clay minerals.…”

Clay-Supported Metal Oxide Nanoparticles in Catalytic Advanced Oxidation Processes: A Review

“…Temperature, pH, and the precursor solvent are crucial factors in determining the particle size and distribution of the metal oxide in clay supports. Research on TiO 2 /kaolinite using titanium isopropoxide demonstrated the role of the DMSO solvent in producing more space for the more homogeneous dispersion of TiO 2 , which furthermore determines the hydrophobicity and reactivity of the nanocomposite [ 97 ]. The impregnation method including wet impregnation consists of mixing a precursor salt with a clay suspension in a solvent and tuning the optimum pH.…”