Macadamia-derived adsorbents for wastewater treatment: a scientometric and critical review

This study presents a comprehensive scientometric and critical review of macadamia-derived adsorbents for wastewater treatment, focusing on their potential as sustainable materials derived from agricultural residues. Given that approximately 70% of macadamia fruit is discarded as waste, this work explores its valorisation as an adsorbent for dyes and heavy metals, aligning with circular economy principles. The review identifies research trends, dominant approaches, and existing gaps in the field. The results indicate that macadamia shell-derived adsorbents show superior adsorption compared with other fruit fractions. While acid activation remains the most used modification method, alkaline activation often results in higher adsorption capacities. Methylene Blue and Cr6+ are the most investigated model contaminants. In terms of modelling, the Freundlich isotherm is predominantly associated with heavy metal adsorption, whereas the Langmuir model better describes dye removal. Kinetic studies indicate that the pseudo-second-order model is the most widely used, accounting for over 70% of reported systems. Scientometric analysis highlights a rapidly expanding research field, with increasing attention to nanocomposites and sustainability-driven applications. Despite this growth, a critical gap is the limited number of investigations on multicomponent systems, which are more representative of real industrial effluents.