Synthesis of palm kernel shells-biochar adsorbent for removal of methylene blue and then reused for latent fingerprint detection using spent adsorbent

This paper reports that a palm kernel shells-biochar (PKS-BC) adsorbent was prepared using a hydrothermal method to remove methylene Blue (MB) and the spent adsorbent was used in latent fingerprint (LFP) detection. The effect of temperature, pH, contact time, dosage, and concentrations on the elimination of MB dye was investigated. Langmuir, Freundlich, Tempkin, and Dubinin-Radushkevich (D-R) models were used to analyze the adsorption isotherm models. The Freundlich model demonstrated an excellent fit to the experimental data and this implied indirect multilayer MB dye adsorption on the heterogeneous surface of the PKS-BS adsorbent. For MB dye, the maximum adsorption capacity was 263.16 mg/g. The adsorption experimental kinetics was investigated using pseudo-first-order, pseudo-second-order, intra-particle and Elovich kinetic models. The results showed that the pseudo-second-order kinetic model accurately explained the chemisorptions of MB dye adsorption on PKS-BC In order to verify the best-fitting isotherm and kinetics models, we utilized the sum of normalized errors (SNE) approach to choose the chi-square test (χ²) error function as a common indicator. The PKS-BC heterogeneous surface and sub-monolayer adsorption process were established by the remarkable correlation between the experimental results and the Freundlich isotherm and pseudo-second-order models. The elimination of MB dye was shown to be an exothermic, spontaneous adsorption process that was viable based on the thermodynamic analysis of (ΔH, ΔG, and ΔS) values. Additionally, MB loaded on PKS-BC (MB-PKS-BC) spent adsorbent was reused as a superior fingerprint powder with the powder dusting approach for the detection of latent fingerprints (LFPs). Under daylight conditions, this spent adsorbent MB-PKS-BC clearly displayed ridge patterns and LFPs images on a variety of surfaces, including glass slides, aluminum foil, aluminum sheets, and tiles. Aged LFP images were also examined for 5 to 20 days on an aluminum foil substrate. These findings suggest that the PKS-BC adsorbent holds promise for the removal of MB dye from wastewater and for reuse in LFPs detection for criminal identifications using the MB-PKS-BC spent adsorbent.