MIL-88A(Fe) as partially-transformative chemically- and physically-active substrate in synthesizing MIL-88A(Fe)/BiOI:Fe with super-adsorption and boosted photocatalysis

Among the various strategies for tailoring nanomaterials, the use of substrates for nanomaterial synthesis (SNS) is a crucial yet often overlooked dimension for controlling nucleation, growth, and final properties. This work introduces a novel approach by strategically employing the metal-organic framework MIL-88A(Fe) as a partially transformative SNS (PT-SNS) to simultaneously dope and structure BiOI, during a one-pot solvothermal synthesis in ethylene glycol at 140 °C. The inherent chemical and thermal instability of MIL-88A(Fe) under these conditions was leveraged not as a weakness but as a functional tool; it partially disintegrated to release Fe³⁺ ions that acted as an in-situ dopant within the growing BiOI lattice (forming BiOI:Fe), while its surface physically acted as a template to profoundly alter crystallization kinetics, favoring nucleation over growth. The resultant MIL-88A(Fe)/BiOI:Fe (M/B:Fe) composite was thoroughly characterized using XRD, SEM/TEM, XPS, BET, DRS, electrochemical techniques, and DFT calculations. Results confirmed successful Fe doping, the formation of a heterojunction with staggered energy-band alignment that facilitated electron transfer, a dramatic reduction in BiOI crystallite size by up to 67 %, and a significantly enhanced surface area of 43.5 m²·g⁻¹, a 230 % increase over the pristine MOF. This synergistic chemical and physical engineering yielded a composite that exhibited a 21-fold and 6-fold increase in photocatalytic rate constant for methylene blue degradation compared to pure MIL-88A(Fe) and BiOI, respectively, and demonstrated super-adsorption behavior with a record adsorption capacity of 1055 mg·g⁻¹. This study successfully establishes the PT-SNS strategy as a promising paradigm, turning MOF instability into an asset for designing advanced hybrid composites with superior performance, paving the way for their application in environmental remediation and beyond. Data Availability: The data used and/or analyzed during the current study are available from the corresponding author upon reasonable request.