Geopolymer-based catalysts for cost-effective environmental governance: A review based on source control and end-of-pipe treatment

Geopolymer is a new type of inorganic polymer materials synthesized by reaction of natural mineral or industrial aluminosilicate solid wastes with aqueous solution of alkali-activator under the curing condition of room temperature or below 100 °C. Many research results demonstrated that the chemical structure and physical properties strongly depended on the raw material chemical composition and preparation conditions. Even though geopolymer as new construction material has been extensively investigated in recent years, the essential brittleness still limits it as commercial building material for the application in the field of municipal engineering. Hence, it was urgent for researchers to explore some alternative approaches. Recently, a number of studies reported that the geopolymers were used as various catalysts for environmental governance. The present review described the latest progresses on the synthesis techniques of the geopolymer-based catalysts in detail, and then focused on the current applications in the environmental governance from the view of source control and end-of-pipe treatment, in which the source control included hydrogen generation, biodiesel production and other heterogeneous catalysis, and the end-of-pipe treatment contained photocatalytic degradation of dye wastewater and gas purification. It is considered that the geopolymer is a promising candidate for recycling of industrial solid waste and developing cost-effective heterogeneous catalysts for environmental governance.