Photocatalytic degradation of lignin on synthesized Ag–AgCl/ZnO nanorods under solar light and preliminary trials for methane fermentation

New photocatalysts, Ag–AgCl/ZnO nanorods, were successfully synthesized in this study by using microwave assisted chemical precipitation and deposition–precipitation–photoreduction methods. The optimal preparation condition was determined as pH 9 in distilled water and 40 min for UV light photoreduction of Ag (i.e. Ag40–AgCl/ZnO) by degradation of methyl orange. This work investigated the feasibility of using Ag40–AgCl/ZnO to degrade lignin under natural solar light and then subsequent methane production with influencing factors like solution pH, dosage of catalyst and initial lignin concentration being considered. OH radicals were found to play the most important role in the photocatalytic process, and the new prepared catalyst possessed stable photocatalytic activity after 7 cycles’ utilization. During the subsequent biogasification, the degraded lignin obtained from 120 min photocatalysis yielded 184 ml methane and 325 ml biogas for per gram of removed total organic carbon, increased by 10.9% and 23.1%, respectively compared to the control.