World orange production is estimated at 60 million tons per annum, while the annual production of orange peel waste is 32 million tons. According to available data, the adsorption capacity of orange peel ranges from 3 mg/g to 5 mg/g, while their water uptake is lower than 1 mg/g. The low water uptake of orange peel and the abundance of biomass in nature has made orange peel an excellent biosorption material. This review summarised different studies on orange peel adsorption of various contaminants to identify properties of orange peel that influence the adsorption of contaminants. Most of the literature reviewed studied orange peel adsorption of heavy metals, followed by studies on the adsorption of dyes, while few studies have investigated adsorption of oil by orange peel. FTIR spectra analysis and SEM micrographs of raw and activated orange peels were studied to understand the structural properties of the biomass responsible for adsorption. The study identified pectin, hydroxyl, carbonyl, carboxyl, and amine groups as components and important functional groups responsible for adsorption in orange peel. Furthermore, changes were observed in the structural properties of the peel after undergoing various modifications. Physical modification increased the surface area for binding and the adsorption of contaminants, while chemical treatments increased the carboxylic groups enhancing adsorption and the binding of contaminants. In addition, heating orange peel during the thermal modification process resulted in a highly porous structure and a subsequent increase in adsorption capacities. In conclusion, physical, chemical, and thermal treatments improve the structural properties of orange peel, resulting in high biosorption uptake. However, orange peels treated with chemicals recorded the highest contaminants adsorption capacities.

Existing soil remediation approaches are lacking in cost-effectiveness, environmental impacts or societal acceptance. Environmental remediation techniques are often characterized by considerable time requirements and may leave residual effects on natural ecosystems, thereby potentially compromising net environmental benefits. This study investigated the oil adsorption capacity of aerogels produced from waste orange peels. Aerogels are highly porous three-dimensional materials made from organic and inorganic materials, with low density and high adjustable specific surface area. Orange peel aerogel was produced from waste orange peels using combined methods of physical, chemical, and thermal modification processes and was dried using the freeze-drying method. Adsorption and reusability tests were conducted after characterization of the aerogel. Surface characterization of the orange peel aerogel indicated it has an ultra-light density of 0.010417 g/cm³, high porosity of 99%, and a measured contact angle of 102°. An adsorption experiment was conducted with sandy and clay soils, and the maximum oil adsorption capacities of the orange peel aerogel were 13.55 mg/g and 9.60 mg/g for sandy and clay soils respectively. High oil adsorption capacity was shown by the produced aerogel and was attributed to its ultra-light density of 0.010417 g/cm³ and high porosity of 99%. In conclusion, the higher oil adsorption capacity of the orange peel aerogel in sandy soil compared with clay soil indicated that soil texture and aerogel properties influenced its oil remediation capacity. The reusability test in three adsorption trials indicated that orange peel aerogel is a sustainable material for the remediation of oil-contaminated soil.

Existing soil remediation approaches are either lacking in cost effectiveness, environmental impacts or societal acceptance. Environmental remediation techniques are often characterized by considerable time requirements, and may leave residual effects on the natural ecosystems, thereby potentially compromising net environmental benefits. This study investigated the oil adsorption capacity of aerogels produced from waste orange peels. Aerogels are highly porous three-dimensional materials made from organic and inorganic materials, with low density, and high adjustable specific surface area. Orange peels aerogel was produced from waste orange peels using combined methods of physical, chemical, and thermal modification process, and was dried using freeze-drying method. Adsorption and reusability test were conducted after characterization of the aerogel. Surface characterization of the orange peels aerogel indicated it has an ultra-light density of 0.010417g/cm3, high porosity of 99%, and contact angle measurement of 102o. Adsorption experiment was conducted with sandy and clay soils, and the maximum oil adsorption capacities of the orange peels aerogel was 13.55mg/g and 9.60mg/g for sandy and clay soil respectively. High oil adsorption capacity was shown by the produced aerogel and attributed to the ultra-light density of 0.010417g/cm3 and high porosity of 99% of the orange peel aerogel. In conclusion, the higher oil adsorption capacity of orange peels aerogel in sandy soil than clay soil indicated that soil texture and aerogel properties influenced the oil remediation capacity of orange peel aerogels. The reusability test in three adsorption trials indicated that orange peels aerogel is a sustainable material for the remediation of oil-contaminated soil.