Adsorption behavior and mechanism of pentachlorophenol on reed biochars: pH effect, pyrolysis temperature, hydrochloric acid treatment and isotherms

• The effect of acid-washed on PCP adsorption behavior was investigated.
• The contribution of two PCP species to the sorption at pH 3.0–12.0 was calculated.
• The π–π and hydrophobic interactions play significant roles for PCP adsorption.
• Adsorption of PCP was inhibited by water extractable DOC from reed biochars.

This study aims to investigate the impacts of pH, inorganic fractions and dissolved organic carbon (DOC) on pentachlorophenol (PCP) adsorption on reed biochars prepared by pyrolysis temperatures ranging from 300 °C to 600 °C, as well as illustrating the adsorption mechanisms. The adsorption capacities for PCP on acid-washed reed biochars were higher than that of original reed biochars. The dedication of neutral PCP molecules (PCP0) and ionized PCP species (PCP−) to the overall adsorption at pH 3.0–12.0 was calculated. The relative contribution of PCP0 was above 53.4% at pH 3.0–5.0, and PCP− was dominant for adsorption at pH 6.0–12.0 with the contributions of 43.2%-100%. The inorganic fractions in the biochars present the negligible or negative effect on PCP adsorption due to its high hydrophilic. The water extractable DOC decreased the adsorption capacity of PCP on reed biochars. The isotherms of PCP adsorption on reed biochars were well described by Freundlich model, and the adsorption mechanisms were mainly interpreted as π–π and hydrophobic interactions. These observations are helpful for exploiting reed biochars as engineered absorbents to remove PCP from aqueous solution.