Highly Efficient Adsorption Characteristics and Mechanism of Nutshell Biochars for Aromatic Organophosphorus Insecticides

The wide use of the insecticide profenofos in crop production has led to serious ecological water problems in agricultural fields. With the increasing global production of nuts, a large amount of nutshell waste has a serious impact on the environment. Turning nutshell waste into biochar to remove high levels of profenofos in water is a cost-effective treatment method. In this study, biochars made from nutshell waste are investigated for the adsorption of aromatic organophosphorus insecticide profenofos. The adsorption amount of nutshell biochar was 13-fold higher than crop stalk biochar in removing profenofos from water. The results indicated that the adsorption of profenofos by nutshell biochar was specific. Scanning electron microscope (SEM) and Brunauer–Emmett–Teller (BET) analysis showed that nutshell biochars had a larger specific surface area and more microporous structures. Meanwhile, nutshell biochars could exhibit a stable adsorption capacity at different initial concentrations of profenofos (10–40 mg/L), temperature (298–318 K), and pH (3–7). Desorption and reuse experiments showed that profenofos was firmly bound to nutshell biochars in water and could be extracted from the biochars with acetonitrile. Within 10 times of recycling, nutshell biochar had a stable and strong adsorption capacity for profenofos. The adsorption process of profenofos by nutshell biochar was pore diffusion and surface adsorption, which is consistent with the pseudo second-order kinetic model and the Freundlich isotherm model. Elemental and Fourier transform infrared spectroscopy (FTIR) analyses showed that the adsorption mechanism of profenofos on nutshell biochar was mainly through π-π and hydrophobic interactions. Nutshell biochar also showed strong adsorption capacity for other aromatic organophosphorus pesticides, and the adsorption rates of methyl parathion, isocarbophos and 2-chloro-4-bromophenol were 85%, 73% and 73%, respectively. Nutshell biochar can serve as an excellent material for removing aromatic organophosphorus insecticide pollution from water