Efficient Removal of Tetracycline and Bisphenol A from Water with a New Hybrid Clay/TiO₂ Composite

Abstract

New TiO2 hybrid composites were prepared from kaolin clay, predried and carbonized biomass, and titanium tetraisopropoxide and explored for tetracycline (TET) and bisphenol A (BPA) removal from water. Overall, the removal rate is 84% for TET and 51% for BPA. The maximum adsorption capacities (q m) are 30 and 23 mg/g for TET and BPA, respectively. These capacities are far greater than those obtained for unmodified TiO2. Increasing the ionic strength of the solution does not change the adsorption capacity of the adsorbent. pH changes only slightly change BPA adsorption, while a pH > 7 significantly reduces the adsorption of TET on the material. The Brouers–Sotolongo fractal model best describes the kinetic data for both TET and BPA adsorption, predicting that the adsorption process occurs via a complex mechanism involving various forces of attraction. Temkin and Freundlich isotherms, which best fit the equilibrium adsorption data for TET and BPA, respectively, suggest that adsorption sites are heterogeneous in nature. Overall, the composite materials are much more effective for TET removal from aqueous solution than for BPA. This phenomenon is assigned to a difference in the TET/adsorbent interactions vs the BPA/adsorbent interactions: the decisive factor appears to be favorable electrostatic interactions for TET yielding a more effective TET removal.

Orange peel biochar/clay/titania composites: low cost, high performance, and easy-to-reuse photocatalysts for the degradation of tetracycline in water

“…Precursors and composites were obtained as described previously; 44 details are available in the ESI. † In short, 1.0 g of biochar and 1.0 g of kaolin clay were dispersed in 30 mL of ethanol, sonicated, then 5 mL of titanium tetraisopropoxide (TTIP) was added and the mixture was vigorously stirred for 1 h. Subsequently, 70 mL of deionized water was added dropwise under continued agitation over the course of another hour.…”

“…16 Recently, we reported the development and performance of a new class of materials based on biochar derived from orange peel (OP), kaolin clay, and titania for the removal of the emerging contaminants (ECs); tetracycline (TET) and bisphenol A (BPA). 44 The NCs have better adsorption capacities for TET (30 mg g −1 ) and BPA (23 mg g −1 ) than the unmodified TiO 2 counterpart or any of the NC constituents (OP biochar, kaolin, titania) alone. Moreover, the composites show a performance that is comparable to some other efficient materials for TET and BPA removal via adsorption.…”

“…A previous study 44 describes the synthesis and the general characteristics of the NCs in detail, including scanning electron microscopy (SEM), elemental analysis (EA), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), and nitrogen sorption (see ref. 44 for full details). SEM showed that the NCs are composed of well-dispersed Environmental Science: Water Research & Technology Paper nanometer-sized titania particles deposited on a porous kaolin clay/carbon support.…”

“…Moreover, the composites show a performance that is comparable to some other efficient materials for TET and BPA removal via adsorption. [44][45][46][47] However, adsorption is a phase transfer phenomenon, and once the active sites are occupied, no further removal of pollutants is possible. On the other hand, in the case of photocatalysis, the contaminants are continually degraded and the fragments are removed from the surface, extending the duration that the surface active sites are available for usein catalytic degradation.…”

“…In this current study, we evaluate OP biochar/kaolin clay/ TiO 2 NCs, but with respect to the photocatalytic degradation of TET under UV and visible light (rather than exploiting pure adsorption, which was described previously 44 ). The choice of TET as a model case for this study is motivated by the extensive use of this drug in veterinary and human Environmental Science: Water Research & Technology Paper medicine around the world resulting in a significant accumulation of TET in freshwater systems.…”