NMDG-Functionalized UiO-66 via PEI Bridging for Efficient Boron Adsorption in Salt Lake Brine

Salt lake brines are a source of boron, but their complex ionic composition presents challenges for adsorption-based recovery. In this study, N-methyl-D-glucamine (NMDG) was introduced into a PEI-containing UiO-66 composite through sequential post-synthetic modification. Structural and spectroscopic characterization supported the incorporation of the organic functional layer, while the characteristic UiO-66 diffraction peaks were retained. NMDG/PEI/UiO-66 showed higher boron uptake than the tested UiO-66 and PEI/UiO-66 controls. At 298 K, the highest experimentally observed capacity was 76.11 mg/g, whereas the Langmuir-fitted limiting capacity was 97.59 mg/g. The kinetic and equilibrium data were described by the pseudo-second-order and Langmuir models, respectively. The material retained approximately 86% of its initial adsorption capacity after three adsorption-desorption cycles and showed boron uptake in brines from Qarhan and Mami Cuo salt lakes. FTIR and XPS observations were consistent with the involvement of the functional layer in boron uptake. These results demonstrate the potential of the NMDG-containing UiO-66 composite for boron recovery under the investigated conditions.