Dual crosslinking of low-methoxyl pectin by calcium and europium for the simultaneous removal of pharmaceuticals and divalent heavy metals

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The contamination of water resources by heavy metals and pharmaceuticals is a significant threat to human health and the environment. Pectin is a promising material for removing heavy metals from water. However, its removal efficacy for other types of pollutants is limited. In this study, we developed a novel approach to enhance the remediation capacity of pectin (with a low degree of methylation) by crosslinking it with different agents: calcium, europium, and their combination. We performed scanning electron microscopy, infrared spectroscopy, and X-ray diffraction experiments to understand the molecular structure of pectin after gelation with the three agents. Our results showed that calcium, europium, and their combination all induce the gelation of pectin. However, the reticulated pectin structures exhibited significant structural differences depending on the type of crosslinking agent used, which affected the adsorption capacity. Specifically, calcium cations partially formed a crystalline “egg-box” structure, whereas europium cations produced a more homogeneous network without crystalline regions. The dual-crosslinking system comprising calcium and europium cations resulted in an intermediate network with both crystalline and amorphous regions. Our findings suggest that dual-cross-linked pectin is a highly effective adsorbent for the simultaneous removal of both heavy metals and pharmaceutical products. This novel approach of crosslinking pectin with multiple agents has the potential to significantly enhance its remediation capacity, offering a promising solution for the simultaneous removal of multiple pollutants from water.