Efficient Adsorbent Derived from Phytolith-Rich Ore for Removal of Tetracycline in Wastewater

Abstract

In recent decades, the tetracycline (TC) concentration in aquatic ecosystems has gradually increased, leading to water pollution problems. Various mineral adsorbents for the removal of tetracyclines have garnered considerable attention. However, efficient adsorbents suitable for use in a wide pH range environment have rarely been reported. Herein, a phytolith-rich adsorbent (PRADS) was prepared by a simple one-step alkali-activated pyrolysis treatment using phytolith as a raw material for effectively removing TC. PRADS, benefiting from its porous structure, which consists of acid- and alkali-resistant, fast-adsorbing macroporous silica and mesoporous carbon, is highly desirable for efficient TC removal from wastewater. The results indicate that PRADS exhibited excellent adsorption performance and stability for TC over a wide pH range of 2.0-12.0 under the coexistence of competing ions, which could be attributed to the fact that PRADS has a porous structure and contains abundant oxygen-containing functional groups and a large number of bonding sites. The adsorption mechanisms of PRADS for TC were mainly attributed to pore filling, hydrogen bonding, π-π electron-donor-acceptor, and electrostatic interactions. This work could offer a novel preparation strategy for the effective adsorption of pollutants by new functionalized phytolith adsorbents.

Figure 1

(a) Schematic illustrating the production of porous adsorbents. (b) SEM images of phytolith. (c) SEM images of PRADS. (d) Mapping of PRADS. (e) TEM images of PRADS. (f) Rietveld refinement results of the XRD data for PRADS. (g) Pore size distribution of pristine phytolith and PRADS.

Figure 2

(a) Fitting to the pseudo-first-order and pseudo-second-order models of PRADS. (b) Fitting to the intraparticle diffusion of PRADS. (c) Equilibrium adsorption isotherms fitted by the Langmuir and Freundlich models. (d) Adsorption isotherms of TC at different temperatures on PRADS.

Figure 3

(a) Effects of pH on the adsorption of TC on PRADS. (b) Effect of coexisting ions on the adsorption performance of PRADS. (c) Recyclability of PRADS for adsorption of TC.

Figure 4

(a) Zeta potentials of PRADS and PRADS + TC at pH ranging from 2.0 to 12.0. (b) FTIR spectra of PRADS and PRADS + TC. (c) High-resolution C 1s spectrum of PRADS and PRADS + TC. (d) High-resolution O 1s spectrum of PRADS and PRADS + TC.

Figure 5

Adsorption mechanism of TC captured by PRADS.