In situ modification provided by a novel wet pyrolysis system to enhance surface properties of biochar for lead immobilization.

• In situ modification while conversion was applied by a novel wet pyrolysis system. • Low content of O 2 would dissolve during pyrolysis due to the liquid/air interface. • Biochar with abundant O- and P- surface functional groups can be produced. • Soaking with Na 2 CO 3 would further enrich carbonate anions on the biochar surface. • As-obtained biochar show an excellent lead adsorption capacity of 316 mg g−1. Surface modification of biochar is significant to obtain more functionalized material for contaminants immobilization. In situ modification, modifying the biochar while the conversion process, was applied by a novel wet pyrolysis system. By using phosphoric acid as working medium, liquid/air interface was created to introduce low content of oxygen, under the control of appropriately settled reaction temperature. Followed with the addition of sodium carbonate to neutralize the system and increase mineral species, effective biochar adsorbent attached with large quantity of acidic oxygenic and phosphoric groups, and carbonate anions was finally produced. The biochar showed excellent decontamination performance of lead with a high adsorption capacity of 316 mg·g−1 and removal efficiency larger than 95%. The alteration of the characteristics after the adsorption confirmed the adsorption mechanism is the bi-function of surface coordination and precipitation. This novel route is easy handling and energy saving, promising it to be a reliable way to produce biochars with attractive surface properties for environmental decontamination. [ABSTRACT FROM AUTHOR]