Synthesis and Characterization of Iron–Silicate–Zirconium Modified Diatomite Reinforced with Multiwalled Carbon Nanotubes as Novel Adsorbent

The development of multifunctional adsorbents from naturally abundant materials remains crucial for sustainable environmental remediation. In this study, iron-silicate-zirconium modified diatomite integrated with multiwalled carbon nanotubes (Fe–SiO₂–Zr diatomite/MWCNTs) was synthesized and characterized via a suite of complementary techniques. X-ray fluorescence (XRF) analysis confirmed the successful incorporation of Fe and Zr, as evidenced by the reduction of SiO₂ from 90.927 wt% in raw diatomite to 75.757 wt% in the composite, with simultaneous increases in Fe₂O₃ (1.856 to 8.692 wt%) and ZrO₂ (0.033 to 10.587 wt%). Fourier transform infrared spectroscopy (FTIR) revealed the coexistence of Fe–O (509.12 cm ^− 1 ) and Zr–O (509.12 cm ^− 1 ) vibrations, Si–O–Zr (965 cm ^− 1 ) linkages, and COO⁻ (1531 cm ^− 1 and 1346 cm ^− 1 ) groups, verifying metal–oxide deposition and covalent interactions with the functionalized MWCNTs. Thermogravimetric analysis (TGA) revealed three-step weight loss totaling 9.42 wt% below 503°C, indicating the elimination of adsorbed water, oxygenated organics, and carbonate residues, with a thermally stable inorganic framework (SiO₂, Fe₂O₃, and ZrO₂) retained. X-ray diffraction (XRD) confirmed the crystalline nature of the composite, which was dominated by cristobalite (82.3%), with secondary phases of fayalite (6.8%), magnetite (6.4%), zirconia (4.1%), and graphite 2H (0.5%), providing strong evidence of successful structural modification and MWCNT incorporation. Scanning electron microscopy (SEM) revealed the transformation of the smooth, porous frustules of raw diatomite into rough, coated surfaces with blocked pores, which was consistent with Fe and Zr oxide deposition and MWCNT adhesion. Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) analyses revealed Type IV isotherm, confirming the mesoporous nature of the composite, yielding a moderate surface area of 46.7 m²/g⁻¹, a low pore volume (0.009 cm³/g⁻¹), and a narrow pore diameter (3.2 nm), indicating partial pore blocking by Fe–Zr oxides and MWCNT networks while retaining a lower-mesopore population essential for adsorption applications. Collectively, these results confirm the successful synthesis of a thermally stable, structurally reinforced Fe–SiO₂–Zr/MWCNT composite with enhanced chemical reactivity, which holds promise for advanced adsorption of anionic pollutants, heavy metals, and dyes in water treatment applications.