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Manganese is one of the heavy metals that is a major environmental concern when present in large amount. Manganese is discarded into water systems by numerous industries, including mining, batteries and electroplating etc. Pineapple leaves were applied as a biomass source to produce a magnetic hydrothermal treated hydochar nanocomposite; Fe3O4-HC. The BET surface area of Fe2O3-HC nanocomposite was 21.27 m2/g. Batch adsorption experiments revealed that the uptake of Mn2+ fit well in the pseudo second kinetics model, while the adsorption isotherm best fit the Freundlich model, with a maximum adsorption capacity of 2.99 mg/g at 25 °C and a pH of 5. The obtained thermodynamic parameters demonstrated that Mn2+ ion adsorption using the Fe2O3-HC nanocomposite was endothermic and nonspontaneous. Additionally, Fe2O3-HC nanocomposite demonstrated to be highly selective towards Mn2+ ions in the presence of other ions. The removal percentage of Mn2+ from a real water sample spiked with 50 mg/L Mn2+ was reported to be 53.2%. The spent adsorbent was then used to detect latent fingerprints, which revealed that Mn2+-Fe2O3-HC nanocomposite generated better and clear latent fingerprints than Fe2O3-HC nanocomposite.

This work provides a novel approach to prepare nitrogen-doped carbon nanoparticles (CNPs) coated on a cerium oxide nanorods nanocomposite (N-CNPs/CeO2NRsnC) for the uptake of cadmium (Cd2+) ions and re-using the spent adsorbent, Cd2+-CNPs/CeO2NRsnC for latent fingerprint detection (LFP). N-CNPs were prepared by a thermal method with urea and cabbage powder as precursors. N-CNPs/CeO2NRsnC was developed with N-CNPs and CeO2NRs with a hydrothermal method and characterized by various instrument methods like UV-visible, FT-IR, XRD, BET, XPS, SEM, and TEM. The N-CNPs/CeO2NRsnC had a greater surface area (9.96 m2/g) than N-CNPs (0.64 m2/g). The synthesized N-CNPs/CeO2NRsnC proved to be a good sorbent material to remove Cd2+ from water at a maximum pH 8 and dosage 10 mg/L. The adsorption was spontaneous and endothermic at 25 ºC. In addition, Cd2+-N-CNPs/CeO2NRsnC has been shown to be sensitive and selective for LFP identification on several porous substrates. It is therefore a good labeling agent for latent fingerprint identification in forensic science.