Intermediate Organic–Inorganic Hybrid with Highly Accessible Pore Structure and Proton Conductivity: Journey from Inorganic Oxide to Metal–Organic Framework

Porous functional materials are highly useful as catalysts, adsorbents, and drug-delivery vehicles. The impact of varying the mole ratio of the organic ligand (BTC, trimesic acid) to iron nitrate on the porosity, surface chemistry, and proton conductivity of Fe2O3-BTC hybrid nanostructures was thoroughly examined. Variation in the BTC content alters the porosity as well as proton conductivity of the hybrid nanoparticles. The improved accessibility of pores and surface area along with functionalization of the surface by trimesic acid was found to be responsible for enhanced and selective dye adsorption. The adsorption capacity of the best Fe2O3-BTC hybrid nanomaterial was 200 mg g–1. The Fe2O3-BTC hybrid nanomaterial provides pH/adsorbent surface charge-dependent selectivity in the adsorption of positive (e.g., methylene blue) and negative dye (fluorescein) from the aqueous solution of their mixture. In addition, the functionalization of pores in the hybrid nanomaterial provides wettability to the pore channels, which allows the protons to conduct through H-bonded water molecules. As a result, the hybrid nanomaterial exhibits enhanced proton conductivity and electrochemical hydrogen evolution reaction. These findings could be useful to develop similar metal oxide–organic hybrid nanoparticles as better adsorbents and electrocatalysts in comparison to the conventional counterparts (i.e., metal oxide or metal–organic frameworks).