Natural organic acid modified alkaline hydroxylated biochar and preparation method and application thereof

The invention discloses natural organic acid modified alkaline hydroxylated biochar as well as a preparation method and application thereof. The method comprises the following steps of: (1) adding acetone into biochar, mixing, carrying out ultrasonic treatment, filtering and washing to obtain clean biochar; (2) mixing the clean biochar with hydrochloric acid, stirring, filtering, washing, and drying at 50-100 DEG C in an inert gas atmosphere to obtain dried biochar; (3) adding the dried biochar into an alkali solution, heating and stirring, filtering, and drying at 50-100 DEG C in an inert gas atmosphere to obtain hydroxylated biochar; (4) adding the hydroxylated biochar into a solution in which natural macromolecular organic acid, absolute ethyl alcohol and a dehydrating agent are dissolved, heating and stirring to obtain a mixed solution; and (5) filtering, washing the precipitate, and drying in an inert gas atmosphere at 50-100 DEG C to obtain the modified biochar. The natural organic acid modified alkalin