Conventional and green-synthesized nanomaterials applied for the adsorption and/or degradation of phenol: A recent overview

Phenol is an aromatic organic compound that is ubiquitous in wastewaters from numerous industries and hugely contributes to water contamination due to its toxicity. Among the studied advanced remediation technologies, adsorption and advanced oxidative processes (AOPs) stand out as promising, feasible and eco-friendly alternative methods. Thus, in this review, a background on concepts of these technologies the sources, impacts and fate of phenol were presented. In addition, the application of conventionally or green synthesized nanomaterials for phenol removal from water and wastewater in the last decade was overviewed. The adsorption capacity and degradation ability of these materials were discussed in terms of kinetic, equilibrium, and thermodynamic studies, operational conditions and percentage of degradation. A special focus was given to graphene-based nanomaterials, which primarily showed efficient, spontaneous and endothermic adsorption that mainly fol-lowed pseudo-second-order kinetics and the Langmuir isothermal model. Besides their great adsorption capacity, they have shown promising performance as a support for nanocatalysts in phenol degradation, especially helping to overcome the main drawbacks of Fenton-related processes. They also showed the great adsorptive capacity and catalytic activity in combined adsorption/degradation systems due to synergistic interactions. Based on the bibliographic research carried out, it can be concluded that, despite growing environmental demands and increasing interest in green technologies, the number of works addressing phenol removal by green materials is still limited. Furthermore, it is noted that there is still a lack of knowledge regarding the practical application of these materials. Thus, the authors recommend that future studies may conduct cost-effectiveness analysis; evaluation of scale-up potential; and subsequent assessment of green materials in terms of regeneration capacity and efficiency in real effluents.