Synthesis and Characterization of MC/TiO 2 NPs Nanocomposite for Removal of Pb 2+ and Reuse of Spent Adsorbent for Blood Fingerprint Detection.

The removal of toxic heavy metals from wastewater through the use of novel adsorbents is expensive. The challenge arises after the heavy metal is removed by the adsorbent, and the fate of the adsorbent is not taken care of. This may create secondary pollution. The study aimed to prepare mesoporous carbon (MC) from macadamia nutshells coated with titanium dioxide nanoparticles (TiO 2 NPs) using a hydrothermal method to remove Pb 2+ and to test the effectiveness of reusing the lead-loaded spent adsorbent (Pb 2+ -MC/TiO 2 NP nanocomposite) in blood fingerprint detection. The samples were characterized using SEM, which confirmed spherical and flower-like structures of the nanomaterials, whereas TEM confirmed a particle size of 5 nm. The presence of functional groups such as C and Ti and a crystalline size of 4 nm were confirmed by FTIR and XRD, respectively. The surface area of 1283.822 m 2 /g for the MC/TiO 2 NP nanocomposite was examined by BET. The removal of Pb 2+ at pH 4 and the dosage of 1.6 g/L with the highest percentage removal of 98% were analyzed by ICP-OES. The Langmuir isotherm model best fit the experimental data, and the maximum adsorption capacity of the MC/TiO 2 NP nanocomposite was 168.919 mg/g. The adsorption followed the pseudo-second-order kinetic model. The Δ H° (-54.783) represented the exothermic nature, and Δ G° (-0.133 to -4.743) indicated that the adsorption process is spontaneous. In the blood fingerprint detection, the fingerprint details were more visible after applying the Pb 2+ -MC/TiO 2 NP nanocomposite than before the application. The reuse application experiments showed that the Pb 2+ -MC/TiO 2 NP nanocomposite might be a useful alternative material for blood fingerprint enhancement when applied on nonporous surfaces, eliminating secondary pollution.