Upcycling Orange Waste into Bio-Based Aerogels

The orange juice industry produces large amounts of by-products. This work introduces new materials based on orange juice side streams─lightweight and high-surface-area aerogels. Orange waste and its fractions (peels, bagasse, and pulp) were first subjected to citric acid hydrolysis, a “green” water-based pre-treatment. Processing parameters (washing with water, biomass fraction, and biomass and citric acid concentrations) were tuned to maximize suspensions’ kinetic stability and produce homogenous aerogels. Soluble sugars removal during biomass washing, along with increased biomass and citric acid concentrations led to higher stability of the suspensions, bearing a pectin-rich liquid phase with a dispersed swollen insoluble fraction. Suspensions’ rheological properties, insoluble contents, and insoluble fractions’ swelling capacities were evaluated. The prepared suspensions were subjected to non-solvent-induced phase separation and solvent exchange with ethanol, followed by drying with supercritical carbon dioxide. Obtained aerogels possessed low densities (<0.1 g/cm3) and high specific surface areas (190–235 m2/g). The insoluble swollen fibers were partially porous and embedded in an open-pore nanostructured network.