Mesoporous carbon spheres via spray drying for selective separation

Pollution control is necessary with the advancement of modern manufacturing industry as various forms of industrial wastes are generated. Adsorption has been considered a safer and less expensive approach for the remediation of environmental damage caused by the release of heavy metal ions, toxic dye molecules or harmful gases. Ordered mesoporous carbon materials are ideal as adsorbents due to their characteristic features including a high surface area, an interlinked pore system with uniform and accessible pores, a tuneable pore wall framework with different functional groups, as well as physical and chemical stability. In particular, uniform ordered mesoporous spheres have great potential for practical applications in dynamic adsorption. The traditional nanocasting approach to synthesize monodisperse carbon spheres involves complex, time-consuming procedures which present difficulties in industrialising the process while the conventional aerosol approach results in polydisperse size distribution, irregular pore sizes and small particle sizes (sub- to a few micrometers). In recent times, the microfluidic jet spray drying technique has been introduced for the synthesis of uniform mesoporous carbon microspheres. However, the characteristics of this class of material and its potential applications have not been fully understood. The main aim of this research was to investigate the ordered mesoporous carbon spheres synthesized from this spray drying technique as promising adsorbents for environmental applications. First, the selective adsorption of the mesoporous spheres in binary dye mixtures was investigated based on the adsorption rate and equilibrium capacity in comparison with that of mesoporous thin film and activated carbon. The results showed that the spherical particles preferentially removed the smaller dye molecule from the mixture, and that the nano sieve layer on the surface of the sphere gave rise to this size exclusion feature. Secondly, the functionalisation of the mesoporous carbon spheres was investigated using a mild oxidant at different durations and temperatures as well as a strong oxidant at different concentrations. Based on the study of the pore evolution, mesostructural stability and surface functionalisation, it was found that the treated samples showed higher adsorption of aniline as compared to the pristine sample. In summary, the findings from these two studies demonstrate the favourable adsorption characteristics of the mesoporous carbon spheres obtained from the unique spray drying technology. In other words, the size exclusion effect on the surface of the sphere resulted in the favourable adsorption as did the tuneable carbon framework for improved interaction with guest molecules. While the adsorption experiments from both studies were conducted in batch condition, this study has broader implications in the application of continuous column adsorption. This research thus opens the possibility for the fast and scalable synthesis of a new class of carbon adsorbent for environmental application.