Emerging water contaminants such as avermectins occur at low concentrations but cause several eco-toxicological effects and are very difficult to remove using conventional water treatment methods. As their presence in water becomes increasingly common due to progressively enhanced usage, there is a need for effective removal technologies. Thus, succinic acid-terminated generation-5 poly(amidoamine) (G-5 PAMAM) was coupled to amine-functionalized Santa Barbara Amorphous-15 (SBA-15-NH2) silica to obtain G-5 PAMAM-functionalized SBA-15-NH2 (or PSBA). This was characterized and employed for low-concentration-solution ivermectin adsorption by investigating the adsorption rate r (15 <= r <= 1440 min), effects of pH (3 <= pH <= 11), concentration C-o (100 <= C-o <= 600 mu g/L), the temperature T (19.5 <= T <= 39.5 degrees C), and reusability at varying temperatures. Adsorption data were described using kinetics and adsorption isotherm models and thermodynamics. The PSBA Fourier transform infrared (FTIR) spectra exhibited typical silanol bands but lost the characteristic silanol hydroxyl group, while gaining -CH and amide-linked bands. The thermal stability was less than that of SBA-15 but more than that of SBA-15-NH2, while both low- and wide-angle X-ray diffraction (XRD) spectra presented typically well-defined structural pore postfunctionalization with the primary SBA-15 structural lattice unchanged in PSBA. The PSBA Brunauer-Emmett-Teller (BET) surface area, pore volume, and size are of intermediate values compared to those of pristine SBA-15 and SBA-15-NH2. The ivermectin adsorption equilibrium was fast (60 min), accompanied by a very fast rate, and >= 81% adsorption occurred within this time. The process is somewhat pH-dependent with dual adsorption peaks at pH values approximate to 3 and approximate to 11. Adsorption was concentration-dependent, increasing accordingly. Adsorption increased with temperature but subsequently decreased with further increase in temperature. The process was spontaneous and overall exothermic with increased disorderliness of ivermectin molecules in solution as the temperature increased. The adsorption models suggested that the process occurred by the transfer of surface electrons, which resulted in electrostatic interactions between the adsorption sites and ivermectin molecules. Adsorption likely occurred at heterogeneous adsorption sites that were energetically distinct, and the process was accompanied by multilayer adsorption on the initial layer of adsorbed ivermectin. Overall, the process was majorly influenced by a concentration-dependent external ivermectin mass transfer. PSBA could reduce ivermectin in low-concentration solutions to approximate to 3.2 mu g/L from a <75 mu g/L solution at any of the studied temperatures. The PSBA adsorption capacity (479.4 mu g/g) is comparatively better than those of most adsorbents currently reported in the literature. The reusability of PSBA is promising for water treatment even after three consecutive reuse cycles with over 84% adsorption capacity retained.
