Chemical and physical properties of Paulownia elongata biochar modified with oxidants for horticultural applications

Treatment of biochar with oxidants such as acids and hydrogen peroxide has been shown to alter porosity, increase adsorption of chemicals, and introduce functional groups on the biochar surfaces, all of which are desirable for their use in horticultural applications. Biochar was produced from the pyrolysis of wood from seven-year-old Paulownia elongata (PE) trees using a top-lit updraft design stove. PE biochar was subsequently treated with 30% (v/v) sulfuric acid, 30% (w/v) oxalic acid, and 10 and 30% (w/w) H2O2. After thorough rinsing with deionized water to remove residual acids and H2O2, biochars were examined for chemical and physical properties. All of the biochars had high carbon percentages, due to the high temperatures (>1000 °C) reached during pyrolysis. Surface areas, micropore surface areas, % micropore surface areas, pH values, cation exchange capacities and electrical conductivities decreased with all oxidant treatments. Analysis of surface functionality by ATR-FTIR showed limited changes resulting from the treatments. TPO/MS analysis showed that all treatments resulted in chars with higher oxidation temperatures suggesting that these are more stable toward oxidation. Unlike reports of biochar derived from different feedstocks and different pyrolysis methods, it appears that treatment of PE biochar with oxidants is unnecessary for its use in horticultural applications.