Geopolymer for use in heavy metals adsorption, and advanced oxidative processes: A critical review

Geopolymer is a ceramic material, most often amorphous; finds applications in fire- and heat-resistant coatings and adhesives, medicines, refractory ceramics and binders, and manufacturing of radioactive waste container. Over the last decade, new cement based on geopolymers has been developed. Most relevant to this review is the fact that its porous nature and chemical similarity to zeolites is being employed for applications pertaining to wastewater treatment. Most of the work has been on the adsorptive treatment of water. However, using chemical reasoning and literature available we show that geopolymers have relevance for further activity on additional areas of relevance to waste water treatment such as photocatalysis, disinfection, and H-2-energy production from waste water etc. These applications would depend strongly on the properties of geopolymers, which in turn would rely on the precursors employed and the synthetic methods used. The relevance of geopolymers for cleaner production is also highlighted. The use of fly ashes and metakaolin composites for the fabrication and surface tailoring of geopolymers (perhaps using relevant surfactants) is suggested as a plausible step in the right direction. Given the critical analysis of the state of the art, and the plausible directions identified, this article will benefit environmental scientists, engineers and chemists interested in deploying geopolymers for environmental remediation purposes. However moving forward, barriers are to be anticipated for the large scale implementation of geopolymers. Several barriers (e.g. legal, economical, technocrats and synthetic challenges) that are likely to hinder future research and translation are highlighted. (C) 2018 Elsevier Ltd. All rights reserved.