Titanium Dioxide–Layered Double Hydroxide Composite Material for Adsorption–Photocatalysis of Water Pollutants

Abstract

Although adsorption has gained favor among numerous water treatment technologies as an effective pollutant removal method, its application is often hindered by challenges with its resource- and energy-intensive regeneration procedure once the available adsorption sites are exhausted. Herein, we present adsorption–photocatalysis composite materials combining layered double hydroxides (LDHs) and titanium dioxide (TiO2) for water treatment. Incorporation of the photocatalyst into the material opens opportunities to harness light from the sun or lamps for oxidative degradation of the adsorbed contaminants on the material surface, to free adsorption sites for material reuse. In addition to allowing photocatalytic regeneration, the addition of TiO2 to colloidal suspensions of delaminated LDH enabled the formation of TiO2–LDH composites with far superior adsorptive performances compared to their parent LDH compounds. During the material synthesis, positively charged LDH layers and negatively charged TiO2 particles combine through electrostatic attraction to yield composites with dramatically enhanced adsorption capacities toward model contaminants, methyl orange and 2,4-dichlorophenoxyacetic acid, by 16.0 and 76.7 times, respectively. Combining delaminated LDH with TiO2 allowed us to maximize the exposure of positively charged surfaces to the contaminants, in a form that can be used as a solid adsorbent. After regeneration, the material regained up to 92% of its adsorption efficiency toward model contaminants. In light of our findings showing significantly different kinetics of adsorption and photocatalytic regeneration, we propose a new scheme to utilize adsorption–photocatalysis systems, in which the two processes are separated to better utilize their unique strengths.

Selective Fluoride Transport in Subnanometer TiO2 Pores

“…This value is close to the transport number of anions in bulk solution, which could be explained by the higher diffusion coefficient of the anions (∼2 × 10 –9 m 2 s –1 for Cl – , Br – , and I – ) compared to the cation (∼1.3 × 10 –9 m 2 s –1 for Na +61 ), indicating that the TiO 2 ALD film shows a negligible selectivity between Na + and these anions. This unselective transport is consistent with the near neutral charge of TiO 2 at the experimental pH (5.7) and implies that there is negligible interaction between TiO 2 and the Na + , Cl – , Br – , or I – ions.…”

Layered zinc hydroxide as an adsorbent for phosphate removal and recovery from wastewater

“…This provides further evidence that electrostatic interaction between the LZH surface and the negatively charged phosphate species did not play a dominant role in the adsorption process as it becomes less effective aer monolayer adsorption. 43 It could be said here that the adsorption of phosphate species was likely not limited to the external surface but the intercalation of the phosphate into the interlayer of the layered structure as well. 25,44 This is further supported by the intra-particle diffusion studies shown in the previous section.…”

LDH-TiO2 Composite for Selenocyanate (SeCN−) Photocatalytic Degradation: Characterization, Treatment Efficiency, Reaction Intermediates and Modeling

“…Furthermore, Paredes et al (2011) [34] report that a TiO 2 /LDH matrix produced a synergistic effect causing both higher •OH radical production and higher degradation of phenol than TiO 2 alone. Similarly, the application of an LDH-TiO 2 matrix for dimethyl phthalate and methylene blue pollutant removal has also been reported [35,36], as well as the use of an LDH-TiO 2 matrix for the removal of 2,4-dichlorophenoxyacetic acid and orange II [37,38]. This clearly indicates improvement in both adsorption and photocatalysis of several aqueous pollutants when using a combined LDH-TiO 2 system.…”