KMnO4-oxidized whole pine needle based adsorbent for selective and efficient removal of cationic dyes.

In the present study, we report the chemical modification of the dried and fallen pine needles (PNs) via a simple protocol using KMnO4 oxidation. The oxidized PNs (OPNs) were evaluated as adsorbents using some cationic and anionic dyes. The successful synthesis of OPNs adsorbent was characterized by various techniques to ascertain its structural attributes. The adsorbent showed selectivity for the cationic dyes with 96.11% removal (Pr) for malachite green (MG) and 89.68% Pr for methylene blue (MB) in 120 min. Kinetic models namely, pseudo-first order, pseudo-second order, and Elovich were applied to have insight into adsorption. Additionally, three adsorption isotherms, i.e., Langmuir, Freundlich, and Temkin were also applied. The dye adsorption followed a pseudo-second-order kinetic model with R2 > 0.99912 for MG and R2 > 0.9998 for MB. The adsorbent followed the Langmuir model with a maximum adsorption capacity (qm) of 223.2 mg/g and 156.9 mg/g for MG and MB, respectively. Furthermore, the OPNs showed remarkable regeneration and recyclability up to nine adsorption-desorption cycles with appreciable adsorption for both the dyes. The use of OPNs as an adsorbent for the removal of dyes from wastewater, therefore, provides an ecologically benign, low-cost, and sustainable solution.

We have carried out the chemical modification of the dried and fallen pine needles (PNs) via a simple protocol using KMnO₄ oxidation. The oxidized PNs (OPNs) were evaluated as adsorbents using some cationic and anionic dyes and the adsorbent showed selectivity for the cationic dyes. As far as the authors are aware, no such report has been documented in the literature wherein an adsorbent based on oxidized PNs with a simple protocol has been used for dye removal.

A two-in-one thiosemicarbazide and whole pine needle-based adsorbent for rapid and efficient adsorption of methylene blue dye and mercuric ions.

Herein, we report the synthesis of an oxidized pine needle-thiosemicarbazone Schiff base (OPN-TSC) from whole pine needles (WPN) as a dual-purpose adsorbent to remove a cationic dye, methylene blue (MB), and Hg2+ ions in separate processes. The adsorbent was synthesized by periodate oxidation of WPN followed by a reaction with thiosemicarbazide. The syntheses of OPN and OPN-TSC were confirmed by FTIR, XRD, FESEM, EDS, BET, and surface charge analysis. The emergence of new peaks at 1729 cm-1 (-CHO stretching) and 1639 cm-1 (-COO- stretching) in the FTIR spectrum of OPN confirmed the oxidation of WPN to OPN. FTIR spectrum of OPN-TSC has a peak at 1604 cm-1 (C = N stretching), confirming the functionalization of OPN to OPN-TSC. XRD studies revealed an increase in the crystallinity of OPN and a decrease in the crystallinity of OPN-TSC because of the attachment of thiosemicarbazide to OPN. The values of %removal for MB and Hg2+ ions by OPN-TSC were found to be 87.36% and 98.2% with maximum adsorption capacity of 279.3 mg/g and 196 mg/g for MB and Hg2+ ions, respectively. The adsorption of MB followed pseudo-second-order kinetics with correlation coefficient (R2 of 0.99383) and Freundlich isotherm (R2 = 0.97239), whereas Hg2+ ion removal demonstrated the Elovich (R2 = 0.97076) and Langmuir isotherm (R2 = 0.95110). OPN-TSC is regenerable with significant recyclability up to 10 cycles for both the adsorbates. The studies established OPN-TSC as a low-cost, sustainable, biodegradable, environmentally benign, and promising adsorbent for the removal of hazardous cationic dyes and toxic metal ions from wastewater and industrial effluents, especially the textile effluents.