Covalent/Metal–Organic Skeleton Composites for Solid-Phase Extraction of Ultraviolet Absorbers in Environmental Samples

In this study, novel covalent/metal–organic skeleton composites (TpBD@MIL-68; 2,4,6-triformylphloroglucinol (Tp) and benzidine (BD)) were combined with high-performance liquid chromatography (HPLC) and used to develop a method for detecting ultraviolet absorbers, including 4-(4,6-diphenyl-1,3,5-triazin-2-yl)benzene-1,3-diol (Appolo-116), 3-benzenediol, 4-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-1 (DBDT), 2,4,6-triphenyl-s-triazine (TPTZ), 2,4,6-trip-tolyl-1.3.5-triazine, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-((hexyl)oxy)phenol (UV-1577), and 2-(4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-(octyloxy)-phenol (UV-1164) is present in greenhouse films and soils. TpBD@MIL-68 has the unique characteristics of a covalent organic framework and a metal–organic framework. TpBD@MIL-68 exhibited a higher extraction efficiency because of π–π and electrostatic interactions between the benzene ring structure of the TpBD, MIL-68, and the ultraviolet absorber molecules. The extraction conditions, including the adsorbent dosage, eluent type and dosage, elution time, and the pH of the sample solution, were fully optimized. The extraction efficiency of TpBD@MIL-68 exceeded 80%. The detection results showed good linearity over a wide range of concentrations (5–5000 µg/L) and low detection limits (0.61–0.94 ng/mL) for target molecules. The practicability of this solid-phase extraction (SPE)–HPLC method was further evaluated by analyzing greenhouse films and soils, with target recoveries of 80.9%–109.9% and relative standard deviations of less than 8.9%. The as-synthesized TpBD@MIL-68 adsorbent exhibited great potential in ultraviolet absorber analysis.