Henrique Moreno

ZIF-8/α-Ag2WO4 heterostructures were designed to investigate electron-driven Ag evolution at MOF–semiconductor interfaces. In situ electron microscopy revealed structural integration and preferential Ag nanoparticle growth on ZIF-8 under irradiation. Interfacial charge redistribution is proposed to mediate this process, offering opportunities for catalytic, sensing, and antimicrobial applications.

The ZIF-8/Ag2SeO3 heterostructure was designed to combine the adsorption capacity and porous architecture of zeolitic imidazolate framework-8 (ZIF-8) with the multifunctional response of Ag2SeO3 (ASO), seeking synergistic interactions that could yield a material with enhanced, complementary functionalities. We report the synthesis and interfacial evolution of ZIF-8/ASO heterostructures and the in situ formation of metallic Ag nanoparticles (NPs) under electron irradiation. X-ray diffraction confirms the coexistence of cubic ZIF-8 (I43m) and monoclinic ASO (P21/c) phases, with a microstructure consisting of ZIF-8 NPs uniformly anchored on ASO microrods in intimate interfacial contact. Time-resolved electron microscopy directly captures the nucleation and growth of Ag NPs on the ZIF-8 surface during electron irradiation, as confirmed by HRTEM-SAED and elemental maps, indicating spatially confined cubic Ag NPs with exposed (111) and (200) planes. Photoluminescence measurements show pronounced emission quenching and spectral redistribution, indicating modified optoelectronic behavior following heterostructure formation. First-principles calculations identify the ZIF-8/ASO(010) interface as a favorable configuration, characterized by strong interfacial interaction and significant charge redistribution. These results are consistent with the experimentally observed localized formation of Ag NPs and suggest that interfacial electronic interactions contribute to Ag+ reduction. Overall, the ZIF-8/ASO heterostructure provides an electron-responsive platform for localized Ag NP formation and interfacial optoelectronic modulation, offering insights into electron-beam-induced processes in ZIF-8-based heterostructures.

Silver orthophosphate (Ag3PO4) is a promising visible-light photocatalyst in which lattice Ag+ ions can be reduced to metallic Ag0 under external stimuli, but the subsequent evolution of these Ag species at heterogeneous interfaces remains poorly understood. Coupling Ag3PO4 with porous, electron-transport-active frameworks such as zeolitic imidazolate framework-8 (ZIF-8) offers a route to modulate this behavior, yet how reduced Ag species migrate across such heterointerfaces remains unexplored. Here, electron-beam irradiation (EBI) combined with time-resolved high-resolution transmission electron microscopy (HRTEM) reveals a previously unreported sequence of structural transformations in ZIF-8/Ag3PO4 heterostructures. Under continuous irradiation, reduced Ag species generated within Ag3PO4 diffuse through the ZIF-8 framework toward its outer surface, where they nucleate and grow into metallic Ag nanoparticles; prolonged exposure then drives their redistribution into the Ag3PO4 matrix, showing that this interfacial silver transport is fully dynamic. Density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations reproduce the early stages of this process, revealing preferential electron accumulation within Ag3PO4, enhanced mobility of reduced Ag species, and the formation of Ag–Ag dimers as nucleation precursors. Together, these experimental and theoretical results establish a mechanism for electron-induced interfacial mass transport in MOF/semiconductor heterostructures, in which ZIF-8 acts not as a passive support but as an active medium that mediates silver migration and reversible interfacial reconstruction.

Ag₂SeO₃ particles were synthesized via a pH-driven sonochemical route (pH = 2, 5, and 12) to elucidate how defect chemistry and morphology govern photocatalytic and antimicrobial performance. X-ray diffraction and Raman spectroscopy confirmed the formation of monoclinic Ag₂SeO₃, while increasing synthesis pH progressively destabilized the lattice, inducing preferred orientation, short-range disorder, and partial segregation of metallic Ag under alkaline conditions. XPS revealed a gradual shift in silver speciation from Ag⁺-dominated lattices toward mixed Ag⁺/Ag⁰ states and reduced lattice oxygen at high pH, consistent with enhanced defect density. Morphological evolution from microrods (pH 2) to shortened rods (pH 5) and sheet-like particles (pH 12) was observed, driven by pH-dependent nucleation and growth kinetics. Optical analyses showed comparable band gaps (∼3.5–3.7 eV), while photoluminescence deconvolution evidenced defect-mediated suppression of charge recombination, particularly for alkaline-synthesized Ag₂SeO₃. Consequently, the pH 12 sample exhibited superior photocatalytic activity toward ciprofloxacin degradation (∼98% under UV irradiation), governed predominantly by ^•O₂H and ¹O₂ species, as demonstrated by scavenger and probing experiments. Toxicity assays confirmed that photocatalytic residues were nontoxic toward Staphylococcus aureus and Lactuca sativa, despite limited mineralization. Antibacterial tests revealed tunable, pH-dependent selectivity: acidic samples favored Gram-positive inhibition, while alkaline samples enhanced Gram-negative activity via synergistic ROS generation and Ag⁺ release. Cytotoxicity and intracellular redox analyses demonstrated concentration-dependent oxidative stress, underscoring the importance of post-treatment separation. Overall, this study establishes pH modulation during sonochemical synthesis as an effective strategy to engineer defect landscapes and multifunctionality in Ag₂SeO₃ for environmental remediation and antimicrobial applications.

The present research examines the photodegradation of sulfamethoxazole under visible light using Ag₂SeO₃ (ASO), synthesized via a sonochemical route in three different reaction environments: aqueous (ASOwat), ammoniacal (ASOamm), and ethanolic (ASOet) . X-ray diffraction, Raman, UV-visible, and photoluminescence spectroscopy measurements were carried out to further understand the structural changes driven by the synthesis̀ medium and their contribution to the photocatalysis. Additionally, field emission scanning electron microscopy revealed significant morphological differences among the samples, which were further confirmed by surface-energy calculations based on density functional theory associated with Wulff constructions. Our results indicate that surface-dependent band gap variations, influenced by the specific surface energy of the exposed facets, may assist in enabling partial visible-light activation, even though bulk ASO exhibits a larger band gap (E_gap ∼ 3.70 eV). The ASOet sample showed the highest performance (∼55% sulfamethoxazole degradation and 54% TOC mineralization) within 120 min. Thus, our work further reinforces the critical importance of particle morphology, which supersedes the overall band gap energy of the material, making visible-light excitation possible even for larger band gap materials.