Auricularia auricula biochar supported γ-FeOOH nanoarrays for electrostatic self-assembly and pH-responsive controlled release of herbicide and fertilizer

The abuse of agrochemicals has caused serious environmental pollution, raising urgently requirement for sensitive controlled release systems. Biochar supported γ-FeOOH nanoarrays (γ-FeOOH@BC) were synthesized in situ through a two-step pyrolyzation-oxidation procedure. The decoration of γ-FeOOH nanoarray structure significantly enhanced the surface positive charge of the composite (pH zpc increased from 2.7 to 7.8), due to which active substances could be electrostatically self-assembled on γ-FeOOH@BC to realize accurate release by changing the environmental pH. The assembled amounts of QNC and PO 4 3- could reach a value of 94 mg·g −1 and 92 mg·g −1 respectively, and the encapsulation efficiency as well as the release concentration were closely related to the pKa of the substance. 45% (QNC) and 63% (PO 4 3- ) could be released at pH = 7.8 and finally both reached to 88% at pH = 11. After 5 rounds of the sensitivity test, QNC/ PO 4 3- could be well assembled or released by pH adjustment, and the encapsulation efficiency remained above 75%. Meanwhile, the assembly structures could also be self-formed in real soil containing QNC/PO 4 3- and had selective herbicidal activity on barnyard grass plants. This work not only provides a feasible material but also a novel method for self-assembly and controlled release of agricultural chemicals.