Optimization of a digested sludge-derived mesoporous material as an efficient and stable heterogeneous catalyst for the photo-Fenton reaction

The anaerobic digestion of sludge has recently received increased interest because of the potential to transform organic matter into methane-rich biogas. However, digested sludge, the residue produced in that process, still contains high levels of heavy metals and other harmful substances that might make traditional disposal difficult. We have devised a facile method of converting digested sludge into a mesoporous material that acts as an effective and stable heterogeneous catalyst for the photo-Fenton reaction. A comparison of the removal of rhodamine B under different conditions showed that FAS-1-350, which was synthesized by mixing the digested sludge with a 1 mol/L (NH4)2Fe(SO4)2 solution followed by calcination at 350 °C, exhibited the best catalytic activity owing to its faster reaction rate and lower degree of Fe leaching. The results indicate that Fe2+-loaded catalysts have significant potential to act as stable and efficient heterogeneous promoters for the photo-Fenton reaction, with better performance than Fe3+-loaded catalysts because the Fe(II)/Fe(III) compounds formed in the calcination process are necessary to sustain the Fenton reaction. This protocol provides an alternative, environmentally friendly method of reusing digested sludge and demonstrates an easily synthesized mesoporous material that effectively degrades azo dyes.

Graphical AbstractDigested sludge-derived photo-Fenton catalysts were synthesized via a facile three-step method. The catalyst produced using ferrous ammonium sulfate in conjunction with a calcination temperature of 350 °C exhibits the best catalytic activity because of its faster reaction rate and lower Fe leaching.Figure optionsDownload as PowerPoint slide