Hydrothermal pretreatment of cotton textile wastes: Biofuel characteristics and biochar electrocatalytic performance

The amount of waste cotton textiles presents an uptrend with the demand for textiles increasing. In this work, hydrothermal pretreatment of waste cotton textiles was conducted at 240 ℃–340 ℃ to obtain bio-crude oil and biochar. The hydrothermal pretreatment at 320 ℃ for 60 min yielded the highest bio-crude oil of 23.3%, in which ketones, diverse oxygen-containing functional group compounds, alcohols, furans, phenols, esters, carboxylic acids, ethers, nitrogen compounds, hydrocarbons and aldehydes were main compounds. Carbon-rich (as high as 76.86%) biochar with low oxygen shows high heating value as high as 30.505 MJ/kg, and lower atomic H/C and O/C ratios, which could be used as alternative solid biofuel. To broaden the utilization of biochar, it was further characterized by SEM, Raman spectra, and XRD. The biochar was the first time to use as electrocatalytic material. It significantly reduced both the overpotential (η10) from 403.6 mV to 247.6 mV and the Tafel slope from 192.5 mV dec-1 to 120.8 mV dec-1. It could speed up charge transfer rate and made H2 release facilely to promote the hydrogen evolution reaction activity with good stability. These results evidence the feasibility of converting waste cotton textiles to high-quality biofuels or even electrocatalytic carbon material via hydrothermal treatment.