This study demonstrated that extraction temperature serves as a critical parameter for modulating the structural characteristics and Pb2+ adsorption performance of natural low methoxyl pectin derived from sunflower (Helianthus annuus) heads, an abundant agricultural byproduct. Pectin extracted at 100 °C for 3 h (AHP) exhibited a lower molecular weight (Mw, 78.2 kDa), higher galacturonic acid (GalA) content (83.32%±3.52%), and lower degree of esterification (DE, 26.34%±1.52%) compared to its low-temperature counterpart (LHP, extracted at 80 °C for 1 h, 84.68%±3.86% GalA, 29.32%±2.18% DE, and bimodal Mw of 316.4 and 115.7 kDa) and commercial citrus pectin (CP, 76.83%±3.74% GalA, 83.24%±3.22% DE, and Mw of 573.1 kDa). Consequently, AHP achieved a superior Pb2+ adsorption capacity of 295.86 mg/g, exceeding that of LHP and CP by 25.7% and 76.6%, respectively. The adsorption process was best described by the Langmuir isotherm and pseudo-second-order kinetic models (R2 > 0.99), indicating a monolayer, chemisorption-dominated mechanism. Integrated characterization using FT-IR, XPS, SEM-EDS, BET and competitive adsorption experiments revealed that the enhanced performance of AHP originated from the synergistic effect of a high content of accessible carboxyl groups and a reduced Mw that minimized chain entanglement. This combination enhanced active-site accessibility and promoted the formation of an open, permeable, ion-crosslinked network upon Pb2+ coordination. This work repositioned extraction from a mere isolation step to a rational design strategy for high-performance biosorbents, offering a sustainable approach to valorize agricultural residues into effective materials for heavy metal remediation.
Peng et al. (Mon,) studied this question.