Water affects the local structure, dynamics, and adsorption properties of metal–organic frameworks (MOFs), yet the molecular-level characterization of confined water remains difficult due to the lack of long-range ordering. Here, we study the water adsorption in microporous MOF Al(HCOO)3 using multinuclear solid-state NMR spectroscopy combined with ab initio molecular dynamics (AIMD) simulations. 1H NMR resolves two distinct confined-water environments and reveals water–framework and water–water contacts. 13C and 27Al NMR further show that water adsorption perturbs the local environments of the formate linkers and AlO6 coordination units. Powder X-ray diffraction shows that the long-range crystalline framework is preserved after water loading, whereas 13C NMR detects a minor mobile formate-containing species that disappears upon re-dehydration, consistent with the partial local hydrolysis of the framework. 2H NMR distinguishes both highly mobile and confined water undergoing rapid anisotropic reorientation. The effective quadrupolar line shape is consistent with rapid anisotropic reorientation, for which C2-axis flips provide one possible motional model. 1H–2H CP-HETCOR NMR further suggests dipolar contacts between restricted water molecules, the formate framework, and neighboring water molecules. AIMD simulations support water–framework interactions associated with the two pore environments and the formation of an interconnected water network. These results provide molecular-level insights into the water adsorption sites and dynamics in Al(HCOO)3 and the previously unreported partial hydrolysis of this MOF.
A concentration-dependent investigation of Fe-doped anatase TiO2 was performed using the full-potential linearized augmented plane wave method implemented in WIEN2k, combined with GGA, GGA+U, and physics-informed neural network (PINN) modeling. Fe concentrations of 3.125%, 6.25%, 12.5%, and 25% were examined using 2 × 2 × 2 anatase TiO2 supercells. Fe incorporation systematically expands the anatase lattice, with the equilibrium volume increasing from 17.14 Å3/f.u. for pristine TiO2 to 18.49 Å3/f.u. within GGA and up to 18.91 Å3/f.u. using Hubbard-corrected treatments at 25% Fe. The bulk modulus decreases from 179.2 GPa to 160.5 GPa in GGA, indicating concentration-driven lattice softening, while the formation energy becomes more negative, reaching −10.91 eV/f.u. for GGA+UTi+UFe at 25% Fe. Electronically, Fe doping introduces localized Fe-3d impurity states within the forbidden gap, narrowing the band gap from 2.18 eV for pristine TiO2 to 1.23 eV in GGA and to 1.59 eV in GGA+UTi+UFe at 25% Fe. The ferromagnetic magnetic moment increases with Fe concentration, reaching 4.41 μB/f.u. for the combined Hubbard correction. Optical calculations reveal enhanced dielectric, conductivity, absorption, reflectivity, and loss responses in the visible-to-near-UV range due to Fe-3d/O-2p/Ti-3d hybridization. The PINN model closely reproduces the FP-LAPW/GGA+U trends, including band gaps from 2.25 eV at 3.125% Fe to 1.48 eV at 25% Fe, demonstrating its usefulness as an efficient surrogate for correlated-property prediction. These results establish Fe doping as an effective route for multifunctional tuning of anatase TiO2 for photocatalytic, photovoltaic, optoelectronic, and spintronic applications.
Removing perchlorate from environmental water can effectively ensure the safety of drinking water and alleviate industrial and agricultural non-point source pollution. Nevertheless, the lack of adsorption sites in the existing adsorbents leads to low adsorption efficiency and low selectivity, which seriously hinders their further application. Here, we report a novel magnetic nanocomposite (Fe3O4@GO@MIL-53(Al)-NH2) constructed on the basis of graphene oxide (GO) and metal-organic frameworks (MOFs, MIL-53(Al)-NH2), as an efficient adsorbent for the removal of perchlorate from real environmental water samples. The Fe3O4@GO@MIL-53(Al)-NH2 achieves efficient and selective adsorption of perchlorate through structure of the GO/MOFs composite. The Fe3O4@GO@MIL-53(Al)-NH2 can be reused for four cycles. Its core advantages lie in: high capacity (23.31 mg g−1), fast kinetics (2-min equilibrium), strong selectivity (anti-interference from co-existing anion ions), easy recovery (saturation magnetization value was 7.0 emu g−1) and high perchlorate removal efficiency (RE%) of 90.2 ± 5.1%, providing an ideal adsorbent for the removal of perchlorate in contaminated water bodies.
Nano-sized zinc ferrite (ZnFe2O4) particles were synthesized via a coprecipitation method, and their photocatalytic performance for the degradation of oxytetracycline (OTC) solution was investigated, both alone and in a ZnFe2O4 photocatalysis/PDS synergistic system. XRD, SEM, and TEM analyses revealed that the as-prepared product consists of well-dispersed, high-purity spinel-type zinc ferrite nanoparticles. XPS spectra showed characteristic peaks corresponding to Zn, Fe, and O. Comparative studies indicated that the ZnFe2O4 nanoparticles alone exhibited weak photocatalytic activity toward OTC degradation, whereas the ZnFe2O4 photocatalysis/PDS synergistic system significantly enhanced the degradation efficiency. Electron paramagnetic resonance (EPR) and radical quenching experiments demonstrated that both radical and non-radical pathways play important roles in the removal of OTC. Under visible light irradiation, ZnFe2O4 generates photogenerated holes, which promote the activation of persulfate, leading to the formation of •SO4−, •OH, and •O2− radicals. Simultaneously, the system facilitates the decomposition of PDS to produce singlet oxygen (1O2). Both pathways collectively contribute to the enhanced degradation of OTC. The optimal initial pH was determined to be 3. Under optimized conditions—100 mL of 50 mg/L OTC solution, 0.5 g/L ZnFe2O4 catalyst, 2 mM PDS, and 90 min of visible light photocatalysis—the degradation efficiency reached 95.15%.
The development of lanthanide-based molecular magnetic materials incorporating organic radicals requires a fundamental understanding of how ligand modification influences magnetic exchange interactions while preserving the coordination environment around the metal center. In this predictive computational study, the electronic structures and magnetic properties of two hypothetical Gd3+ complexes with donor–acceptor semiquinone–nitronylnitroxide biradicals, Tp2Gd(SQNN) (1) and Tp2Gd(SQPhNN) (2), were investigated using ab initio calculations and compared with the previously characterized monoradical complex Tp2Gd(SQ); Tp is hydro-tris(1-pyrazolyl)borate. For the first time, the related zinc complex TpCumZn(SQNN) (3) was also computed using its experimental geometry, providing a reference point for the reliability of the computational protocol. The inclusion of dynamic correlation at the NEVPT2 (N-Electron Valence State Perturbation Theory, 2nd order) level was essential for correctly predicting the antiferromagnetic nature of the Gd3+–biradical interaction, while the SA-CASSCF (State-Average Complete Active Space Self-Consistent Field) alone yielded a ferromagnetic ground state. The computed exchange interaction in the –2J formalism between Gd3+ and the biradical in complexes 1 and 2 (J ≈ –2.1 cm−1) is more than two times weaker than that in Tp2Gd(SQ) (J = –5.4 cm−1). The intraligand exchange parameters JSQ–NN = 690 cm−1 and JSQ–PhNN = 122 cm−1 reflect strong ferromagnetic coupling within the biradical moieties. Application of the valence bond configuration interaction model yielded electronic coupling matrix elements HDA of 15,283 cm−1 and 6546 cm−1 for the yttrium analogues of 1 and 2, respectively. The calculated magnetic susceptibility data for complexes 1 and 2 closely resemble the behavior of Tp2Gd(SQ), although the characteristic temperatures differ due to the unequal exchange coupling strengths. This study demonstrates that modern computational methods enable consistent prediction of the key magnetic characteristics of heterospin systems based on their possible molecular structures.
