Design of Biomass-Based Composite Photocatalysts for Wastewater Treatment: A Review Over the Past Decade and Future Prospects

Abstract

Biomass-based composites (BCPs) have been investigated for more than one decade as photocatalysts for pollutants´ water treatment, however their technological application remains restricted. The systematic review performed aims to exhibit the latest advancement in photocatalytic degradation of pollutants in aqueous solution by BCPs synthesized with biomass and TiO2 and/or ZnO, and to identify the necessary steps to achieve BCPs large scale application. Multivariate data analysis approach was performed to identify trend relationships between the BCPs synthesis method, the experimental conditions, and the BCPs characteristics correlated with the observed removal efficiency and the photodegradation kinetics. The results indicated the relevance of adsorption processes on the pollutants removal efficiency, reflected by the principal component analysis (PCA) performed on all categories of pollutants (PCA_pol). Furthermore, the PCA applied to textile dyes (PCA_dyes) and pharmaceutical compounds (PCA_pharma) also indicate the influence of variables related to the composite synthesis (i.e. thermal treatment and time spent on BCPs synthesis) and photocatalytic experimental parameters (catalyst concentration, pollutant concentration and irradiation time) on the degradation kinetic accomplished by BCPs. The characterization of composites reveals that the specific surface area and the narrow band gap are key characteristics for BCPs to serve as a competitive photocatalyst. The stability and recyclability of the BCPs are also discussed as necessary properties to overcome the experimental/lab scale phase and to move to full-scale applications. Further investigations are recommended to assess the performance of BCPs when treating real water, compared to commercial catalysts, as well as cost evaluation.