Characterization of biochars derived from various spent mushroom substrates and evaluation of their adsorption performance of Cu(II) ions from aqueous solution.

A total of 16 biochar adsorbents were produced from four types of spent mushroom substrates to investigate the effect of pyrolysis temperature and raw material composition on the Cu(II) adsorption performance of the resulting biochars. It was determined that the pyrolysis temperature and substrate composition markedly influenced the thermal stability, the degree of carbonization, surface functional group content, and structural morphology of the biochars, but did not affect the adsorption isotherms or kinetics. Optimal results were obtained with an initial pH of 5, adsorbent dosage of 1 g/L, Cu(II) concentration of 50 mg/L, and temperature of 25 °C. The four best-performing biochars conformed to the Langmuir isotherm model and followed pseudo-second-order kinetics with maximum Cu(II) adsorption between 52.6 and 65.6 mg/g. Precipitation was the dominant mechanism for Cu(II) adsorption onto Lentinus edodes spent substrate-derived biochar pyrolyzed at 600 °C (LESS600), whereas complexation with surface functional groups was the prominent mechanism of Cu(II) removal by Auricularia auricula spent substrate-derived biochar pyrolyzed at 500 °C (AASS500). The Flammulina velutipes and Pleurotus ostreatus spent substrate-derived biochars pyrolyzed at 600 °C (FVSS600 and POSS600, respectively) removed Cu(II) ions using both precipitation and Cu-π complexation interactions. The findings indicate that biochar derived from spent mushroom substrates containing abundant lignin and pyrolyzed at high temperatures (500 or 600 °C) demonstrate effective Cu(II) removal because of the various physico-chemical properties discussed herein.