Application of Magnetic Fe3O4 Alnus glutinosa Sawdust Biochar/SiO2/CTAB as a New Sorbent for Magnetic Solid Phase Extraction of Heavy Metals from Fruit and Waters Samples

The coating of magnetic Fe3O4 Alnus glutinosa sawdust biochar with SiO2 and further functionalising by cetyltrimethyl ammonium bromide (CTAB), a cationic surfactant, was described for the first time in the current paper. The magnetic Fe3O4 Alnus glutinosa sawdust biochar/SiO2/CTAB(MAGBC/SiO2/CTAB) was implemented to separate and preconcentrate the Cu2+, Cd2+, and Pb2+ions efficiently in waters and a number of fruit samples by solid-phase extraction (SPE) method. Adsorbent characterisation was realised by fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Fundamental factors affecting the extraction yield of the analyte ions including solution pH, adsorbent amount, sample volume and desorption contact time were fully researched and optimised as 8.0, 0.25 g, 500 mL and 60 min, respectively, and the eluent was specified as 5.0 mL of 0.1 M of HCl solution. The adsorption equilibrium eventuated after 15 min of contact time and it was noticed that the chemisorption mechanism was dominant upon the analyte ions adsorption. The limits of detection (LOD) were calculated as 0.24, 0.62 and 1.55 µg L−1 and the limits of quantitation (LOQ) were determined as 0.81, 2.08, and 5.17 µg L−1 for Cu2+, Cd2+, and Pb2+ ions, respectively. The relative recoveries (RR%) were in the ranges of 93.3–103.4%, 92.5–102.8%, and 91.8–101.9% for Cu2+, Cd2+, and Pb2+ ions, respectively, while the relative standard deviations (RSD%) were obtained lower than 4.0% (n = 10) by applying the method at optimised conditions. The maximum adsorption capacities of MAGBC/SiO2/CTAB were obtained as 123.7, 80.0 and 118.5 mg g−1for Cu2+, Cd2+, and Pb2+ions, respectively. Consequently, the developed new, simple, rapid, sensitive, and economical SPE method based on MAGBC/SiO2/CTAB was successfully implemented to waters and some of the fruit samples to determine the Cu2+, Cd2+, and Pb2+ions simultaneously.