**Moawia O. Ahmed \*, Ameen Shrpip and Muhammad Mansoor**

Chemistry Department, College of Science, Taibah University, P.O. Box 30003, Al Madinah Al Munawarah 41477, Saudi Arabia; shrpip@hotmail.com (A.S.); mansoorishaque@hotmail.com (M.M.) **\*** Correspondence: moahmed@taibahu.edu.sa; Tel.: +966-5655-48322

Received: 25 January 2020; Accepted: 18 February 2020; Published: 21 February 2020

**Abstract:** A new type of silica hybrid material functionalized with Schiff base-propyl-thiol and propyl-thiol groups (adsorbents **1** and **2**, respectively) was synthesized using a co-condensation method. The synthesized materials and their starting materials were successfully characterized using a variety of techniques such as Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption–desorption isotherms, the Brunauer–Emmett–Teller (BET) surface area calculation method, the Barrett, Joyner, and Halenda (BJH) pore size calculation method, thermogravimetry analysis (TGA), and 1H and 13C nuclear magnetic resonance (NMR) spectra. The results indicate that the new material (adsorbent 1) has a large surface and possesses different functional groups (-SH, -OH, -C=O and –N=C). The newly synthesized hybrid materials (**1** and **2**) were investigated as potential adsorbents for removal of toxic heavy metals, such as Pb(II) from aqueous solutions. The adsorption results show that materials **1** and **2** have different sorption properties and were found to be effective adsorbents for Pb(II) removal from aqueous solutions. In addition, compound **1** exhibited a higher adsorption capacity for Pb(II) compared to compound **2**. The results showed that the optimum pH for Pb(II) sorption was 6.5. Contact time was observed to occur after 30 min for 25 mg L−<sup>1</sup> Pb(II) concentration and adsorbent dose of 0.4 g L−<sup>1</sup> at 25 ◦C.

**Keywords:** heavy metals; hybrid materials; functionalized; Schiff base; lead; Langmuir and Freundlich
